Glitching

hey can someone explain me how to get in boxes
i know how to get in with my legs but not how to get full in it, plz help me

After you're halfway in, move forward and crouch.

...doesnt matter? you should stand and hold shift when you walk back and forth. when you're halfway in, move forward and crouch.
Jumping up in air using crouch seems to be fine, I havent tried that way, I jump in air holding shift (standing up)