They are tricky, and pretty unique as a feature in English.
Phrasal verbs don't have to be demons when you look at this site! The Online Writing Lab is a great help too for ESL/ESOL students.
Stanford University offers this bibliography of how and when to use the things. A good simple definition which will not get you into too much trouble. At the end of 2002, I was reading about a French girl named Severine. She was 23 years old and had trouble making a natural and idiomatic English. A taping of her conversation with the examiner and friend was on TOEFL Farm. Does anyone remember this site and where it went?
If I can't find the Farm - and it seems to be gone - I will give you this humourous link instead.
TEFL Farm as I remember it: be careful, this is a web archive. The humourous link which I promised you earlier!