Glad you like it! :) The grappling hook can be used at specific spots where a white "!"-icon popps up. You have to press Q on your keyboard and select the grappling-hook from the menu to activate it. I have to admit it's a bit convoluted, but I'm working on a simpler solution for a future update :)
Have you set the "Battle Tutorial" option to ON? You should have gotten a tutorial on the action commands. Basically you have to hit enter as soon as the two circles overlap. Hope this helps!