Para
1) Purpose - ...if you could say "in order to" in english... (Purpose) (She studies to - in order to - become a doctor.)
2) Recipient - If you mention the recipient.... (I made this cake for you.) (These flowers are for them.)
3) Destination - If you are talking about a destination... (We are going to/towards Spain.)
4) Specific Time / Deadlines - If you are talking about deadlines... (Specific Time) (I need that project by Monday.)
Por
*** - If not 1-4...