Just put inert sand or gravel. Aquarium pea gravel for example.
The Microsorum pteropus and Anubias spp. grow attached to rock or wood, so use thread to tie each one down gently to a stone and they will root over it.
The elodea (Egeria densa) can just be left to float of you can put the stems into the gravel if you prefer.
Plants are use light as an energy source so that they can 'feed' off inorganic molecules. So basically they are feeding of nutrients in the water, but they need light to do so. The water changes provide the nutrients (as the plants use up nutrients in the water it needs to be changed frequently) , and you will need to place the tank on a windowsill or have a small (preferably florescent) desk lamp to provide light for the plants. If you use a light, keep it on for around 12 hours a day.