Use 'chime in' when you want to join a conversation, especially if it's informal. They were chatting about the new movie, so I chimed in with my review.
Pro Tip 2/3
Avoid Overuse
Don't overuse 'chime in'; it can seem like you're dominating the conversation. She chimed in so often, others couldn't speak.
Pro Tip 3/3
Group Discussions
'Chime in' is great for group discussions to signal that your turn to speak has come naturally. In the meeting, wait for the right moment to chime in with your thoughts.