To release the foot pedal, first raise the red lock into the unlock position (green). 
Gently lift the foot pedal upwards to open the clamping mechanism. The clamps will spring (!) into a vertical position. 

Give the trunk a straight and even cut. Set the trunk in the center of the stand over the spike. Make sure the trunk and spike have contact but do not use force. Do not drill a hole into the trunk.

Push down the foot pedal. Repeat pushing until the clamping mechanism securely fastens the trunk.
When tree and trunk are well positioned and securely fastened, slide the lock into the red position (locked) to secure the foot pedal.
Add tap water to keep your tree fresh. Slowly fill the tank with tap water until the level indicator is clearly visible. Stop adding water. Always keep the inner container filled with tap water.