A:
🌺The meaning depends on the context but it's generally used when you are trying to get someone to do something you expect them to do.
Example:
You are hesitant to eat foreign food because it looks really spicy. Your friend said it's not too spicy and so he or she urges you to eat by saying: "Come ooonnnnnn, just do ittt. It's not that hot."
🌸Another way to use it is when you just want to complain about something/someone that you think is acting dumb or bad.
Example:
Your game is taking a long time to load, you get frustrated from waiting so long and complain out loud to no one, "Come on! 😡 Why isn't it working?!"
🌼An informal way to use it would be the equivalent of 'hitting on' or 'flirting with' someone.
"Are you flirting with me?" = "Are you coming onto me?