'Cut up' is a common English idiom and phrasal verb, with an unfortunate number of meanings, some of them fairly random. Depending on context, it may refer to:
1. v., adj. A variant of 'cut into pieces'. "I cut up the apples." / "The cut up apples will turn brown."
2. v., adj. To hurt someone, especially to wound with a knife or other sharp object. "Mess with me, boy, and I'll cut you up." / "The car accident left him pretty cut up."
3. v. To criticize severely. Probably a metaphorical adaptation of #2.
4.adj. To feel upset or guilty. "She's pretty cut up about it."
5. v. To act silly or wild; to clown around. "Edward liked to cut up in class." This meaning is sometimes used as a noun using the forms cut-up or cutup; "he's a real cut-up."
6. v. (UK) To pull sharply in front of someone in traffic. "He cut up a bus." / "That bastard cut me up!" This is not used in the USA, where one would use the phrase 'cut off' instead.
7. n. A series of clips taken from a TV series or movie, often used as a 'best of' or 'worst of' reel. See 'clip show'.
To further confuse matters, it is often used as a separable phrasal verb, meaning that it can appear in the form "cut X up", as in "I cut the apples up", and "The car accident cut him up pretty badly." For those who are not native English speakers, this has the effect of making it look like "up" is a useless word that can be senselessly stuck in random places.