I bought something similar a couple of months ago from a german vendor. It's a clay container that is rectangular and about 10 cm wide x 20 cm tall x 2 cm deep and therefore suitable for hanging from a mesh with other flat mounts. They also sell completely round (i.e tube-shaped) containers that are better for hanging like a like a small hanging basket. The advice I was given is to fill it with water (I use RO) and leave it be until a natural layer of moss develops and then it's ready to use. They use it successfully for orchids that need constant moisture all year round and have no natural dormancy (i.e. Dendrobium cuthbertsonii and most of the smaller pleurothallids). So far my container has developed a "nice" thin layer of algae and black mould. I think I'll have to attach a little bit of moss myself otherwise I'll be waiting for years before I can use it.