Game has following modes:

Classic

Crush the cubes of the same color by tapping one of them if they are in a block of 3 or more. A block can be formed in minimum of 3 cubes.
Connectors are introduced randomly from top which will help you to connect either vertical or horizontal cube blocks of different colors.
Coins are introduced on board for each 100 cubes are crushed. You will need to set out the coins at the slots to clear the level.

Clear All

You will need to clear the board by crushing all cubes. No new cubes are added from top, but you may run into deadlock if not played wisely!
Bombs are introduced to help you clear the level which would crush all the cubes surrounding it. It will blast off the all cubes surrounding the bomb.

Filled

Complexity will increase as the new cubes will get filled from bottom and you would need to make hurry to finish the level. If the level of cubes reaches the top, you are gone.
Bombs will help you often to clear out the level. It would blast off the cubes same as in "Clear All" level.
No time limits to complete the level but instead some number of cubes are crushed and you are done to next level!

Timed

This is almost same as "Filled" mode but there are time limits to complete the levels.
You need to complete each level in maximum of 2 minutes and that should be enough!

Endless

This is almost same as "Classic" mode but there are no limits. Keep playing until you put it aside!