To Stuff In
To Cram In, To Pack
transitive verb, ichidan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means stuffed, this word means to stuff in, as in you're doing the stuffing. You know this because you're a mail (める) carrier, and you always have to stuff mail into people's packed mailboxes. Why don't these people check their mail more? It’s hard work trying to cram in all this junk mail!
詰める refers to tightly fitting something into an available space, like cramming clothes into a suitcase, putting jam into a jar, or even scooting over to make room, as you're squeezing yourself into a narrower space.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned that reading with the kanji, so you should have no troubles here.
たくさんの服をスーツケースに無理やり詰めました。
I forcefully stuffed a lot of clothes into the suitcase.
あんまり詰めすぎると、ファスナーが閉まらなくなるよ。
If you overpack it, the zipper won't close.
すいません、もう少し詰めてもらえませんか？
Excuse me, could you move a bit closer together to make some space for me?
お弁当にご飯を詰めといてくれない？
Can you put some rice in my bento box for me?