Keyboard:
~~~~~~~~~
F2     - toggle animations
F4     - test level
F5     - load level
F6     - save level
F7     - set checkpoint
F8     - restore checkpoint
F9     - change width/height of the level
F10    - change background
Ins    - Insert an new object
Del    - Delete an object
a      - mark all
RShift - Move faster
LShift - Add object to selection
Esc    - Leave the editor
Cursor keys - Move marked object around

Mouse:
~~~~~~
left   - move or mark an object
middle - mark rectangle 
right  - scroll around

For more info, have a look at the info documentation.