Why these keyboard/mouse shortcuts won't work?

[^GoJo^]

I got a few (or a lot?) of shortcuts that does not work. For example, switch between windows of the same app : i press the key combo i choose (tried multiple) and nothing happens (no matter which app i use).. I got a logitech mouse, intalled their pref pane and chose back/forward for side buttons : nothing happen when i press them, wether it's on finder, safari, etc.. Why is that?!