〜て ＋ 置く
is used to imply that an action is in preparation of something in the future. It comes from て置く, 'putting something ready (in advance)'
テストの復習しておく I will review the test (for the future)
日本語の辞書を買っておいた I bought/will buy a japanese dictionary (in anticipation of needing it in the future)
車を修理しておきます I will repair the car (for future use)
といて is a request for someone to do something in advance.
～とく Abbreviation
止めておこう 止めとこう。 Let's stop (before it gets out of hand)