Class trees are displayed in tree buffers which install their own major mode. Most Emacs keys work in tree buffers in the usual way, e.g., you can move around in the buffer with the usual C-f, C-v etc., or you can search with C-s.
Tree-specific commands are bound to simple keystrokes, similar to
Gnus. You can take a look at the key bindings by entering
? which calls
M-x describe-mode in both tree and member