Columns is derived from Tetris, as it involves arranging falling blocks in such a way as to clear them.
However, in columns they are groups of 3 same-size but varying color blocks, which must be arranged into sequences of 3 or more, either horizontally, vertically or diagonally.
Sequences of 4 or 5 count for double or triple points, and diagonal sequences score the most.
The real trick is to set up 'combos' - where one line causes other blocks to drop so as to create other lines.

More information about Columns on MobyGames.