"Want" (hustereo) means to be deficient, suffer need, be in need & is used only here & Mk12:44.

Paul could say this confidently because he had counted all things to be loss in view of the surpassing value of knowing Christ Jesus his Lord Phil3:8 Mk12:44 out of her poverty

FOR I HAVE LEARNED: ego gar emathon (1SAAI): (3:8; Ge28:20; Ex2:21; Mt 6:31-34; Lu3:14; 1Ti6:6-9; Heb10:34; Heb13:5,6)

How did he learn? God's class "Discipline 101" or "Tribulaton102" (Ro5:3) which He graciously & patiently teaches all of His "students" so that they might become sharers of His holiness (Heb12:10) & after they are trained that their lives would bring forth the peaceful fruit of righteousness (Heb12:11). (see section on discipline in Heb12:5-11).

"I did learn"--looking at his long experience as a unit. Paul had come to understand and accept the teaching that Christ was His sufficiency as true and to apply it in his life. This word is related to the root word MATHETES, disciple. So it reflects one who learns intentionally by inquiry and observation. E.g., Jesus' disciples had left all to follow Him and they learned by watching Jesus interact in REAL-LIFE situations; e.g., His clear example of teaching on humility in Jn13:15,16,17. "If you know these things, you are blessed if you do them.''Mt11:29 learn (AAImp)

“have learned” are in a construction in the Greek which speaks of entrance into a new condition. It is, “I have come to learn.” Paul had not always known that. He had been reared in the lap of luxury, and had never known want as a young man.

HOW TO BE CONTENT:en ois eimi (1SPAI) autarkes: autos + arkeô = be self-sufficient = word expressing one of the favorite Stoic doctrines = that man should be sufficient to himself for all things; able, by the power of his own will, to resist the shock of circumstance. Paul is self-sufficient (bc he is "Savior-sufficient") through the power of the new self = not he, but Christ in him.

Paul is teaching here that he had learned how to be independent of external circumstances. Paul had come to the point of realizing JESUS is ALL he had and he thereby learned that JESUS was ALL he NEEDED! Socrates said as to who is wealthiest: "He that is content with least, for autarkeia is nature's wealth." [2Co12:9] ''My grace is SUFFICIENT (ARKEO = will suffice, is enough) for you...''

IN WHATEVER CIRCUMSTANCES I AM: einai (PAN):

Wuest comments that "the “I” is emphatic. It is, “I, for my part, whatever others may feel.” The word “content” is the translation of a Greek word used by the Stoic school of philosophy which taught that man should be sufficient to himself for all things. It means “to be independent of external circumstances.” It speaks of self-sufficiency and competency. But Paul’s self-sufficiency was not of the Stoic kind. It was Christ-sufficiency. Paul’s independence was not Stoic independence, but dependence upon Christ. He found his sufficiency in Christ. He was independent of circumstances because he was dependent upon Christ.

"I know" (eido) means to perceive or have understanding. The perfect tense speaks of a completed action in the past with present ongoing effect or result, and so speaks of the permanence of his "knowing".

how to continually be humbled or abased...how to be brought low...how to be depressed.

AND I ALSO KNOW HOW TO LIVE IN PROSPERITY: oida (1SRAI) kai perisseuein (PAN):

in presence of abundance, abounding richly. "If you can't be happy with what you already have, why should God trust you with anything else?" Good question. Far too many people go through life chronically unhappy with their circumstances. Yet in every situation those who are IN CHRIST have whatever they need to be content (if not happy). When we focus on material things, we will often feel frustrated, but when we focus on the Lord, we can rejoice that what we have can never be taken from us.

IN ANY & EVERY CIRCUMSTANCE I HAVE LEARNED THE SECRET: en panti kai en pasin memuemai (1SRPI): (Dt32:10; Ne9:20; Is8:11; Je31:19; Mt11:29; 13:52; Ep4:20,21)   “I have been very thoroughly initiated into the human lot with all of its ups and downs” (NEB).

"Learned the secret" (“I have been initiated, I possess the secret”) (mueo is the root word for mustes meaning "one initiated" which in turn is the source of "mystery" or musterion) was a technical term referring to the initiatory rites required of any person who wished to enter into the secrets and privileges of the ancient mystery religions. It means to learn the secret of something thru personal experience or as the result of initiation. Once again Paul appears to borrow from the vocabulary of his pagan environment just the right word that would be readily understood by his readers to express the precise idea he wished to impart. He does not mean to say that he automatically knew the secret of a contented life. but that he came to know this secret through a difficult process that could be described as an initiation.  Paul was saying that he had been "initiated" through disciplining circumstances into the "MYSTERY" of Christ in Him the hope of Glory (cf Ac9:18-20). When he was born again he was possessed all of Jesus he would ever possess but it was through the variegated circumstances of his life that the Spirit was able to teach him that Christ was his very life and his continual source of power.

Paul represents the "abundant" Christian life as a mystery, the secrets of which are taught by God the Holy Spirit to the soul that longs to prove in its own personal experience “what is that good and acceptable and perfect will of God.”

Vine adds that "learned the secret" is "in the passive voice, (which speaks of action exerted on one from without or from an outside force, in this case of course the Spirit of God taking Paul from glory to glory) “I have been initiated,” and the perfect tense (past completed action with present ongoing result or effect) conveys the thought of the abiding effects of the initiation. Paul’s use of this word indicates that this constant and complete contentment, whilst possible to all believers, involves many and varied testings, costing self-denial, demanding fervent prayer and abstention from many a thing which might be considered not only legitimate but consistent with improved circumstances. Such contentment brings present peace and future reward." The effort called for to learn the secret reminds one of Paul's instruction to Timothy to "have nothing to do with worldly fables fit only for old women. On the other hand, discipline (gymnazo -command to make this a habit of your life, literally to train in the gym stripped of all clothes which would encumber one's training!) yourself for the purpose of godliness (train yourself, keeping yourself spiritually fit) for bodily discipline is only of little profit, but godliness (spiritual training) is profitable for all things (in everything and in every way), since it holds promise for the present life (life that now is, literally "the now life") and also for the life to come ("of the coming future life")." (1Ti4:7-8)

OF BEING FILLED AND GOING HUNGRY: kai chortazesthai (PPN) kai peinan (PAN):

"Filled" is chortazo derived from chortos (grass, hay) and so to fatten like an animal.

"Going hungry" (peinao is from peina =hunger is related the word penes which is the poor man who has to work for his living) means famished, starved.

BOTH OF HAVING ABUNDANCE AND SUFFERING NEED: kai perisseuein (PAN) kai hustereisthai (PPN):
 

I CAN DO ALL THINGS: panta ischuo (1SPAI): (Jn 15:4,5,7; 2Co3:4,5)  (Macarthur on Php4:13)

THROUGH (in) HIM ("in Christ") WHO (continually) STRENGTHENS ME: en toi endunamounti (PAPMSD) me:(2 Co12:9,10; Ep3:16; 6:10; Col 1:11; Is40:29-31; 41:10; 45:24) 

Christ continually ''pours'' His supernatural power into Paul to enable him in each circumstance. To pour power into one.