To Put In
To Load Something
transitive verb, ichidan verb
You know the kanji 込 means into. This verb is transitive, meaning you are doing the action. If you “do something into something” you are putting it into that thing. So this means to put in or to load something.
Lucky for you, the reading you learned with the kanji is the one you use here. In case you need a hand with the okurigana, here’s a mnemonic for you:
You always try to put in your emotions into the mail (める) you send. You don't just load your mail with words, but also with emotions, to make it truly heartfelt mail.
ショットガンに弾を込める時間がなかったんだ。
I didn’t have enough time to load rounds into the shotgun.
もっと気持ちを込めて演技しろよ！それでもプロの劇団員か？
Put more emotion in your performance! Are you really a professional theatrical actor?