Hello
@Camillalarsson74 Open the Play Store from the Launcher.
Browse apps by category there, or use the search box to find a specific app for your Chromebook.
After you've found an app, press the Install button on the app page.
The app will download and install to your Chromebook automatically.
It will now appear in the Launcher.
Otherwise I recommend you first try a factory reset and see if that solve your problem.