Incarnum has2 main parts to the mechanic.  The first is the "essentia pool", or Mana, or MP, or however else you would like describe the point system. Incarnum races get bonus points.  Takinga  feat that requires essentia to activate provides bonus points.  This pool is always active.  IT does not get diminished as the day goes by.

The second part to the mechanic is recepticles.  The book calls these "racial abilities", "feats", "soulmelds", and "chakra binds".  At the beginning of a day, an incarnum character determines his/her soulmelds/chakra inds for the day.  This is like spell selection.  No essentia points are expended.

On his/her turn, a character can redistribute his/her essenia points to his/her recepticles.  It should be noted that 4 to 6 points is the usual max per recepticle.  Essentia is neve burned.  It is simply redistributed.

For example:  Let's say a character has a racial speed ability (+5' per essentia point), a feat (+1d6 damage while raging per essentia point), and a soulmeld (+1 fort saves per essentia point).   He has 9 essentia points.

This means he can gain +15' move, +3d6 while raging AND +3 to fort saves (three points each).  On his turn, he can elect to lose his fast movment for more damage by moving points over.

The system allows for huge flexibility, while establishing a cap of 4 to 6 max points allowed into any essentia recepticle.

Well, on the flip side, you'd be able to do 4d6 or 6d6 every round.  Otherwise, you can do 6d6 for 5 rounds. and then no more abilities for that day.