NOTE: Most people use Backup To DVD/CD/Flash.
It will ask for the name of a file to save the download in on your hard disk. Normally you use the name and folder it suggests. After saving it, find the download file in Windows Explorer and double-click it to install it.
The downloaded copy will work without any limitations for 90 days, after which you may get into the program and explore its various features, but you may not actually make a backup.
If you decide you like it, you can purchase an unlimited use license. You will receive a license ID to enter into the software to disable the expiration date, whether or not it has been passed yet.
You can install Backup To DVD/CD/Flash and Backup Made Simple on the same computer. They should be installed in the same folder if you do.
If you have an earlier version of the software you will normally install it in the same folder and upgrade the old software. There is no need to uninstall the old software first, though doing so will remove the old software from the "Add/Remove Programs" list on your Windows Control Panel, which neat minded people will appreciate.
Old and new versions may coexist on your computer simply by installing them in different folders. If you do so the global settings on each backup type will be stored separately for each copy, so they may be different if you change them in one copy but not the other. The instructions on which folders and files to backup up are NOT affected the same way - they are always shared. Note that if you install them side by side this way and then uninstall one, you will have to reinstall the other for it to work again. You will not lose any folder and file instructions if you do this.