This is a charade - two separate parts are joined together to form the answer.
Look for a video game (3 letters) that needs to be reversed, then add a word meaning 'practice' (5 letters). The colon separates the wordplay from the definition.
Answer: MISUSAGE | SIM (simulation/video game) reversed gives MIS, plus USAGE (practice) = MISUSAGE (that's not right/improper use)