The menu on the right of that main page is how you enter into the data.
It looks like this -
Once you choose a category, keep clicking on the picture for finer and finer grained information.
Always one to give thanks on my blog, "James Rosindell devised the OneZoom concept and developed the software. He received regular advice and support from Luke Harmon who co-author of the OneZoom manuscript. Yan Wong has provided advice, software for data collection and helped at events. Laura Nunes helped at events and wrote labels for the bird tree. Duncan Gillies assisted James Rosindell in the supervision and recruitment of Kai Zhong who is now a full time software developer for OneZoom."