Installing for the first time:
WaveShop is distributed as a zip file containing an installer. Unzip the distribution file, using WinZip or an equivalent program, and then double-click on WaveShop.msi to launch the installer. The installer is about as simple as an installer can be: just keep hitting "Next." Note that on the "Select Installation Folder" page, you have the option to install for all users, but the default is to only install for the current user.
Upgrading a previous installation:
Note that double-clicking WaveShop.msi won't work: you will get the message "Another version of this product is already installed". If you're connected to the Internet, you can upgrade to the latest version via Help/Check for Updates.