Php 4:10 But I rejoiced in the Lord greatly, that now at the last your care of me hath flourished again; wherein ye were also careful, but ye lacked opportunity.
Php 4:11 Not that I speak in respect of want: for I have learned, in whatsoever state I am, therewith to be content.
Php 4:12 I know both how to be abased, and I know how to abound: every where and in all things I am instructed both to be full and to be hungry, both to abound and to suffer need.
Php 4:13 I can do all things through Christ which strengtheneth me.
Paul is again thanking them for their kindness, and also pointing out he will survive regardless. He knows how to be content and joyous in Christ, regardless of what is going on in his life.
I saw an interesting misapplication of the last verse in some documentary a few years ago. A woman with severe physical handicaps was attempting to do something that most completely healthy people can't do, and she used this verse as evidence of why she would succeed. She failed. Of course, anything is possible with God, but it must be God's will, and not our own. If God willed it, I could sustain an impact from a semi in my street. He can do anything, because He is God. It would still be incredibly stupid of me to go stand in front of a semi though, because I have no evidence God's will towards the laws of physics have changed for me today. Barring any divine communication, I have to assume that the will of God toward rules like gravity, force, inertia, etc is the same as it is the rest of the time. We can't force God's will to comply with our will. It doesn't go that way.