If you still can't figure out this simple system here is a picture walkthrough
1. Get your grenade
2. Turn the pin the opposite way the arrow goes on your spring motor
3. When you have cranked to the desired amount, pull down on the pin so the top tan clip locks into the white snowflake connector
4. Fill with "shrapnel"
5. Toss grenade so it lands with the pin(gear side) hitting the ground
Tan clip unlocks, motor engages and shrapnel goes flying everywhere. The last picture doesn't do it any justice, but you get the idea.
If you have any questions, you can message me and I will try my best to help you.