Open your service, then the Apps tab.
1. Find the app. There is a search box above the catalogue, and the apps are grouped into sections - Websites, Databases, AI, Developer Tools and so on.
2. Check what it needs. Each card shows the memory the app wants and how many containers it starts. An app that needs more memory than your plan allows is marked before you choose it.
3. Press Install on the card. A box opens underneath where you can give it a name - leave it empty and it is named after the app.
Installing downloads the app, which takes anything from a few seconds to several minutes for larger ones. You can leave the page while it works.
When it is done the app appears in Your Apps with a Running badge, and you can start, stop, restart or remove it from there.