Start installing Omnitapps4 by running the executable, for example Omnitapps Composer (64 bit) 4.0.0.0.exe
You have to accept the terms in the License Agreement to be able to install Omnitapps4.
Omnitapps4 is installed in the "C:\Program Files\Prestop\Omnitapps Composer (64 bit)" folder.
Your configurations will be stored in your "Documents" folder under "Omnitapps Composer". Initially there will be nothing here, Omnitapps4 installs it's template and default configurations the first time you will run Omnitapps.