cheer somebody up means make somebody feel happier (e.g. You look so sad! Cheer up!)
cheer up means be happier (e.g. She cheered up when she heard the good news.)
chip in ,exams help (e.g. If everyone chips in we can get the kitchen painted by noon.)
clean up/ clear up/ tidy up something means make it clean, tidy etc. (e.g. Look at this mess! Who’s going to tidy up? (or tidy it up))
clear up means become bright (for weather) (e.g. It was raining when I got up, but it cleared up during the morning)
close down/ shut down means stop doing business (e.g. There used to be a shop at the end of the street: it closed down a few years ago)