Mouse and key bindings (i.e. keyboard shortcuts) are implemented with Openbox. LXDE users should follow the Openbox wiki to edit ~/.config/openbox/lxde-rc.xml.
An optional GUI for editing the key bindings is provided by the obkeyAUR package. While it edits rc.xml by default, you can direct it to the LXDE configuration as follows:
$ obkey ~/.config/openbox/lxde-rc.xml