While in a Match3 level you can use coins to purchase power-ups. Power-ups are useful to help you clear the board if you find yourself in a tough spot without using moves.
If you fail a level you can purchase extra moves with coins. This will provide you with 5 extra moves and in some cases bursts on the board if you have failed multiple times in a row.
Boosters can be purchased before playing a level. These will place the chosen booster on the board prior to the level starting.