The aim of Blobs is simply to fill the little gauge to the right labeled "Blobs." Once you do this, you'll cleared the level and you're off to the next.
To fill it, you have to get rid of the little colored balls you place on the playing field (yep, those are the "Blobs"). One blob gotten rid of equals one step further towards the goal. To place the blobs simply click with the mouse, the blob under "next" to the right will then be placed on the playing field.