Hi Fang! -Welcome to the forum
I've never owned an A4000 myself, but I seem to recall that every amiga has these keyboard shortcuts to move the mouse-pointer around with:
D = Directional keys (Cursor keys)
Amiga = The key(s) with the Amiga logo on
Alt = The button that says "Alt"
L = Left (To explain wich of the Alt buttons to use)
R = Right
Amiga + D = The pointer moves in the selected direction
Shift+Amiga + D = As above but in big steps
LAlt+Amiga = One Left mouse-button click
RAlt+Amiga = One Right mouse-button click
The button clicks needs to be kept pressed down if you navigate in menus etc. And of course dubble hitted when dubble clicking on eg. icons...
Good luck!