If you choose java fern or java moss, you don't bury those in the substrate. Instead, you tie them to things, like driftwood or another decoration, and they'll grow roots that hold on to the objects. Many other plants you bury in the gravel. I hear that some people have problems with roots getting tangled in the under gravel filters, so plants like java fern may be your best choice.
This site has pictures of plants, and if you click on them it brings you to a pretty good description of them.
To give you some idea how to start, here's what I do when I get a new plant:
---Bring the plant home (duh)
---Soak it in a potassium permanganate solution until it turns from purple to brown (you can also soak it in a bleach solution, I think I've read 1 part bleach to 20 parts water, for a half hour).
---Rinse really well (use water with extra dechlorinator if you used bleach)
---Put it where you want it in your tank, planting it in gravel or tying it (I used plain old sewing thread) to a rock, decoration, or driftwood
---If your fish are really curious, they'll probably rearrange them anyway, lol!!