First, attach the separate black plastic piece to the seat post. The black silicon band will stretch to hold it in place BUT, you have to pull the band firmly. It is meant to be a tight fit so there will be as little movement as possible to get the best brake response. Then hold the light firmly in one hand and pull back the lever. Do not worry, you will not break it! As you pull it back, push the light up and the light will attach to the bracket with two definite clicks. Make sure you hear them, for a solid fit. When you detach the light from the bracket, pull back on the lever, push the light down firmly and it will come free.