to paraphrase, think:

Indica~Stoned/couchlock (body)

Sativa~High/trippy (mental)

to be even less accurate you could think like Sativas are uppers and Indicas are downers.

I know that these are not technically close to accurate, but for a beginner it might be easier for you to think that way until you can further differentiate between the two sub-sets. If you ever need info about drugs/plant effects, erowid (see Shovelhandle's link) is one your best friends. Very reliable information.