Blocks falling in a column.

I'm pretty green when it comes to C# and I am trying to make a 2d single block game similar to tetris. My troubles are that I can't figure out how to make my blocks fall, aligning down an invisible column that will keep them straight. I'm looking to have about 8 columns for the blocks to fall in to. With the spawner I have now, if blocks land on top of eachother they will most likely be off to one side. I have been looking for tutorials that demonstrate similar ideas, but have been unlucky so far in finding any. Any help is much appreciated.