I am working my way through tutorials, but the whole package / repo terminology even in Yast is not simple.

I think I installed an application, but can't seem to find it. Is there a simple way to see what apps are installed? Thank you.

*Edit: I downloaded the RPM, and in Dolphin right clicked on it and went through one menu level to install it. Something happened quickly, too quickly to read, and then disappeared. I can't find the app any obvious way. Don't know if it was installed or not. Don't know how to list the ones that are installed.