You can only clear a block if its made up of two or more squares. When you clear a block, those above drop down. The blocks also move to the right when columns are emptied. Beware you dont end up with marooned blocks!
Bigger blocks score more points, single blocks left at the end cost you lives. It's not frantic and there is no time pressure.
The game is written using Microsofts C# language using their free development platform "C# Express".
The file is stored on my Sky Drive (Thanks Microsoft! )