Help! Complete beginner with dying plant!

Hey, a friend gave me a plant about 3 weeks old since sprouting, and I've just been keeping it in a coffee can on my windowsill and watering it almost every day. I need help quick, because the leaves have been dying and a few little ones have even fallen off. It was getting drowned for about a day, which i think might have led to the dying, but i'm not sure. Is the problem the lighting (im just using the sun shining through the window, should i switch to a lightbulb over it?), or something else, and is there any way i could save it? any help would really be appreciated

I'd get it out of that coffee can and into something that drains out the bottom. Re-pot into something bigger with good dirt. The sun will be enough to keep it alive, but the days are getting shorter sending you into flowering. Lights would help keep it constant.

Careful not to water too much. wait till the soil is dry before watering

yeh the window sill is okay for a little while, but sooner or later you had to know you were either gonna have to plant it outside or hook yourself up with some cheap compact flourescents. Just make yourself a nice simple growroom out of a cut up cardboard box and some duct tape and a black trashbag, n do it up in your closet - itll give you enough room if you partition off about 2-3 square feet for each plant you have, and then as it gets older just keep tying down the branches by drilling little holes into the lip of your new pot, and using sewing thread or yarn and looping it into the holes, wrapping it around your branches, and tying it up. Keepin the plants low is a HUGE advantage spacewise. My plants are goin into week 4 of flowering here in a few days, and tied down, they are almost under 1 foot. seriously, just by like an inch or so BARELY over a foot, when untied and stretched out they would be almost 3 feet. It works man. N good luck with your grow.