It's fairly explicitly spelt out in the spell itself. It does not take more than 1 complex action, but it is a series of opposed tests.
First, you roll your spellcasting test against your target's Strength + Body to levitate your unwilling metahuman projectile. If you win, you can then move him to your heart's desire, in Force * net hits meters per turn. You choose to throw him at his good buddy in range, which is treated as a Ranged Attack test, so said good buddy gets to roll Reaction as normal against the spellcasting test you already made. If he fails to get out of the way, you inflict a number of Stun boxes as decided by your GM. Now, according to Arsenal, a metahuman body used as an improvised weapon deals his Body as stun damage, so that troll actually makes a fantastic metahuman battering ram.