This is the default control's mapping. You may change it within the settings of the game by selecting "Control Settings" in the Options Menu.

In Game Actions:

Arrow Keys - Move
Z Key - Jump
X Key - Shoot
C Key - Slide
A - Select Previous Weapon
S - Select Next Weapon
Enter - Pause Menu


In Menu Actions:
Arrow Keys - Select
Z Key - Confirm Selection
X Key - Cancel Selection


If you plugged in a controller in the middle of running the game, it may not be autodetected.
You can press F3 to have it get detected without needing to reboot the game.