transitive verb, godan verb
You know that 詰める is "to stuff in" and the kanji 込 is into. When you’re stuffing something into something else, you are going to stuff or to cram it in.
Just as in English, this word can also be used in a figurative sense, like cramming knowledge into your head.
This word uses the readings you learned with the kanji. If you remember your kanji readings, you'll be fine here.
I managed to cram all my clothes into my suitcase.