What you downloaded was a zip file. Before you can use the contents, it will need to be extracted.
Go to the file you downloaded using explorer. It should be called DDOCharGen3122.zip. Right click on that file to bring up the menu. Go to "Extract All". This will bring up a box asking you for a directory. Select whatever Directory you want the program to go to and hit Okay.
The program and all it's files will then decompress. You can now use Explorer to go to that directory and run the Executable (it should be called DDOCharGen.exe). Just double click on that file to start up the program. You can create a desktop shortcut if you like to make it easier to get to.
The extraction is a one time thing, you only need to do it once, or whenever you download a new version of the planner. Once it is extracted, from then on you only need to run that executable to start up the program.
"They laughed when I said I was going to be a comedian ... They're not laughing now." - Bob Monkhouse