Worms Blast is based on shooting a coloured bazooka at various coloured blocks. If the colours match, the block is destroyed, along with all connecting blocks of the same colour. Hurrah! If the colours don't match, then the weapon colour splats all over the block you hit and those immediately surrounding it.
Blocks come in also sorts of shapes and sizes. Standard blocks are probably the only ones you've got a good mental picture of right now, so feel free to let your thoughts wander to the possibilities of Dead blocks, Bouncy blocks, Anchor blocks, and lovely Rainbow blocks.
Mac OS 9.1 or Mac OS X 10.1.3 or later