If you don't have enough gravel in your tank and don't want a thick layer of gravel for planting plants, then you can get a terra cotta pot to plant it in. Fill up the terra cotta with gravel, take the plant out of the pot it came in, pull off the rock wool that's around its roots (if you don't it tends to somehow come to the surface and float around in little bits all over your tank), and bury it in the gravel in the terra cotta so its about at the same depth as it was in the pot it came it (too deep and the plant can rot, too shallowly and the roots will be exposed). Then put the terra cotta in your tank. If you don't have a terra cotta pot and extra gravel right now, just leave the plant in it's pot in the tank until you have time to attend to it; it'll be fine.