To select a function, press the middle key (called Navi by Nokia) and use the up and down keys to select a submenu -- and so on, until you get to a function you want. Finally, pressing the Navi key activates the function.
The C key is used to correct errors.
The top line (as on the Nokia) shows the equivalent short cut code. To use a short cut code, ensure the Nokia is in Standby (e.g., by pressing C several times), then press the central Navi key, then press the appropriate digits for the short cut code.