The Grapple is a block action, you do have to roll Might to initiate it. That's a normal action.
Then the target, on it's next action, get's to try to act and maybe break the grapple.
Now it's your turn again, you can either maintain the grapple, with all the possibilities that gives you (damage, maneuvers etc.)
or you can chose to release the grapple and make a full attack, which would include the possibility of throwing the target.
See YS 211:
Finally, you can also release the grapple if
you want to roll a standard action instead, like
making a full attack, performing a maneuver, or
throwing the opponent (basically forced move-
ment, to a maximum of one zone). The target
gets a defense roll, as usual.
So 1 Action to "grab and hold" + 1 Action to "throw at wall"