Media describe on SupraBank in which environment the interaction is taking place for instance in a solvent (e.g. water) or buffer (e.g. PBS). Often the media are not pure and contain additives (e.g. NaCl).
Solvents, Additives and Buffers are loaded in the interaction creation form. Most of the time you do not have to add new parts in these sections, except you created a unique buffer for your experiments.
SupraBank takes interactions in other media into account, and contineously tries to improve the avaiable media.