If I got a plant and put it in a small pot or jar with some gravel, (My tank floor only has rocks), and provided it with a lot of light, is that all you need to take care of the plant? Gravel and light? Do you have to add any nutrients or anything?

edit: and you buy them at petstores, yes? Do they come in seed form?

depends on the plant. Heavy root feeders would benefit from gravel with a buried fertilizer tablet. Stem plants like anacharis would do fine in gravel only.

I agree, it totally depends on the plant. Some don't even need gravel, they attach to things like rocks and wood and don't need a ton of light (this would be java fern, java moss, african fern, anubias). Some don't need a lot of light but still need a decent amount (2wpg or so) and like some fertilizer (hornwort, anacharis, hygro, watersprite, etc). Others need a lot of light, others need heavy root feedings, some need CO2, some need... the list goes on.

So if you want to keep it simple try things like java fern and anubias, either of those could be attached to something and you wouldn't even need the pot of gravel. These can be hard to find locally sometimes, but search out local fish clubs (often people are selling or giving away trimmings) or you can buy some online if you dont' mind spending extra $$ for shipping charges. These sort of plants grow pretty slow though, so if you are impatient they might not be the right thing for you.

If you have more lighting, like say 2 watts per gallon, you have a lot more options, but the problem with goldies is they like to eat several varieties of plants...