Suggest you read the manual (I think they still come with one).
double click for on, takes you to High, press button to cycle to Medium (if applicable), Low and then back to High. When on, hold button for 2sec? for flash. Hold longer for off.
When off hold for 5sec? to enter settings mode. Starts at 1, press to go through, if you dont press for 2sec? it set it in that mode and turns off.
In reflex you will get full lumens if moving, its drops down if not. So to test in garden shake it for 5-10 seconds then rest it on a bin or wall, you can watch it power down as it senses no movement.