How to obtain coins

You can obtain coins through many ways.  The easiest way is that every time a new even occurs, you will get coins just by clicking on them.  Once you do that, the next batch of coins will be earned by playing games.  You will earn a certain amount of coins based on your performance in the game and then some bonus coins if its your first win of that event.  However there is a set limit on how many coins you can earn from each event. You can also get coins from the brawl box or a coin booster than will double the amount of coins you own for a limited time.

What to do with coins

Coins are the primary currency in Brawl Starts but can only be used to by crates.  These crates will contain a variety of prizes including coin boosts, upgrade tokens, coins, and brawlers.