I think I bought an app I didn't mean / want to buy and I don't know what it is

I Just downloaded the upgrade to "Catalina" and I got a message that my 32 bit apps (MS Word and Excel) are no longer compatible. They told to check the App Store, which I did and in the upper right of the screen it had a button labelled "in-app" . I don't know what that meant, so I clicked on it to find out and it told me that I just bought an app. I did not want to buy an app yet and I don't even know what I bought. How can I find out what I bought and what in-app means. I'll want to update my MS Office programs at some point but I'm not ready yet - if that's even what I "bought"

didn't mean / want to