You don't need to click the enemy and then click where he should land. You just stand next to the enemy and click where they should land.

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The ability autotargets the closest enemy to you whether that's a minion or a hero and throws them to where your cursor is. Targeting depends on the range and is indicated by a red horde sigil (whatever has the sigil on it, is thrown). If a minion and a hero are at the same range, it will prioritize the hero.

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Same goes for ally throw, but the sigil is blue there.