Im new at this and need help!!

[Rusty Trichome]

someone told me i was over watering it so should i let it dry out?

Cannabis prefers a wet-dry cycle. But if you let the soil dry too much, it tends to reject water and let's it flow straight to the drain holes. If this does happen, add water very slowly, a cup at a time. It'll re-condition the medium. Don't let it get that far too often, though.
Conversely, wet roots rot. So do not allow it to sit in standing water and no habitual oversaturation.

can i cut the yellow leaves off?

Nope. She'll discard them when she's done using them. Once she does drop 'em, get 'em out of the pot. Bugs will want to breed there if you don't.

should i buy some plant food?

If you're serious about growing your plant(s) then you'd better start shopping for nutrients right now. Some good cannabis nutrients come in 2-part or 3-part "systems". Some of the more commonly used, (common and reliable) are Botanicare, Canna, Fox Farms...

However, with improper lighting, your efforts will fall short. With a window grow, you only have limited sunlight, and are you keeping her dark periods absolutely dark? No kitchen or bathroom lights interrupting her sleep? If not, you're stressing the crap out oif her, and it will only get worse when in flower. A dark closet, some nutrients and some CFL's would benefit your efforts. :thumbsup:

Crap. I took too long. I see you've just addressed the lighting thing. :thumbsup: