To Get Into, To Go Deep Into
intransitive verb, godan verb
This word ends with the hiragana う, which tells you it's a verb. The kanji 込 means into, so the verb version is to get into. This word generally attaches to the stem of another verb, and adds a nuance of moving something towards the center of something, or going deep into something. You’ll be seeing lots of examples of words with 込む on the end, so you’ll gradually get a feel for the nuance it adds!
こむ
Lucky for you, the reading you learned with the kanji is the one you use here.
ここではプールに飛び込むのは禁止です。
Jumping into the pool is prohibited here.
男は強盗を両手で押さえ込みました。
The man restrained the robber with both hands.
サトミはしばらく考え込んでいました。
Satomi was lost in thought for a while.