～ておくTo do something in advance

When the conjunction particle て is followed by the う-Verb 置(お)く in Japanese, it regularly has the meaning of 'to do (A) in advance'. 置(お)く as a verb itself means 'to place something' (down), but also has the nuance 'to leave something alone', or to 'drop something' (like a topic). In this way, ておく can be thought of as meaning 'to do (A) and leave it (until later)'.

When using ておく, the 'future event' that the (A) action is being done for may be something that is coming soon, or may be something that the speaker doesn't want to ever come. Due to this, ておく is also regularly used when the speaker is doing something specifically to prevent another thing from happening.

Caution

ておく is sometimes contracted to とく (or どく in verbs where て would usually be said as で). Although this is not excessively common in conversation, it is very common in drama, manga, and similar media.