Verb + にいく

JLPT Level: N5
Meanings

to go to do something

to go somewhere in order to ~

to go for the purpose of ~

Usage

V-ます-stem + に行く

する → しに行く

う-verbs: ぬ/む/ぶ/ぐ/す verbs follow the same pattern by using their ます-stem + に行く

Explanation
Verb + にいく expresses going somewhere specifically for the purpose of doing the action of the verb. It focuses on the purpose or goal of the trip, rather than simply moving from one place to another. The verb before に goes into its ます-stem form, and に行く attaches to that stem to indicate going to do that action. For します verbs, you use しに行く (e.g., 勉強しに行く). The construction is commonly used for planned activities or activities undertaken away from the speaker’s current location.
学校へ勉強しに行く。
がっこうへべんきょうしにいく。

I go to school to study.

買い物をしに行く。
かいものをしにいく。

I go to shop for shopping.

友達に会いに行く。
ともだちにあいにいく。

I go to meet my friend.

日曜日は日本語を勉強しに行く。
にちようびはにほんごをべんきょうしにいく。

On Sundays I go to study Japanese.