The library catalog is, in fact, rather difficult to search topically. If you know the author or the title of the item you want, it is pretty straightforward. Searching for a topic, however, is, in fact rather difficult. This 6-minute video takes off, essentially, where the library tutorial ends. It is dense and probably won't make much sense unless you have spent time searching OSCAR already or have done that tutorial!
Use this URL to connect to it: https://youtu.be/l4NyuaRsAZI