I currently only have a few tracks stored on my SSD - so it is relatively easy to find the one I want to play next.
But once I have many tracks … how does one search?
For instance: my “Roon My Tracks” list has columns for:
… which one does the Search work on?
In the Track browser, you’d be better off using the Filter function (the “funnel” icon) in the column headers (e.g. the Track, Album artist, Artist, Album headers). The gearwheel icon allows you to customise which attributes you want to have displayed in the Track browser list.
The Search function in Roon is a global function - it searches everything in your library and beyond, if you subscribe to streaming services as well.
Thanks, Geoff.
I’ll have a look at that, tomorra. 
Just to add, you can also use the Focus feature of Roon in the Track Browser. This gives another way to slice and dice your collection. A Focus selection can also be stored in a Bookmark for fast future reference.
In addition to Geoff’s fine advice, just to be clear: The global search itself is the magnifying glass icon that’s top right on every page. (Note that it’s being improved by Roon and there are vast discussions about this. In the current state, try to not make typos or leave out or add spaces, it does not deal well with that. So, finding things you don’t know exactly how they are spelled can be a challenge. It will get better, Roon has the proper framework in place now)
This thread has some good tips for finding stuff as well:
Thanks for your help, guys. 