To ask God for HELP, comfort, healing, forgiveness, REPENTENACE,  etc. 

We also pray to give God thanks, praise, glory, etc.

Basically to communicate with God, to develop a relationship that God has desired since creation.

Man is hardwired to pray.  In Genesis we learn that we are made in Gods image.  Prayer was our first speech/communication with God. 

Often we only seem to pray when we are in trouble.  Consider this, because we are human and we sin, aren’t we in trouble all the time?  Therefore shouldn't we be praying more than we do?