What you need to do is hit the enemies with your 3 and then grab them with your 1 while they're still stunned. Repeat four more times in a single match for a total of five stun/grab combos.
This is a pretty good combo so you should get this without having to try but if you're having trouble a mode like arena where giant clusters of enemies are together. Maybe team up with other Gods that have stun attacks and then stun after their stun then go for the grab.