I've just posted a couple of articles on SQL Shack, the Apex SQL community website. The first post introduces Dynamic Management Objects and how we can use them to monitor SQL Server, it's an entry level read and introduces some T-SQL fundamentals along the way.
Then I've followed up that post with an article focusing on sys.dm_exec_requests. This is a very common DMV to use as it shows all active requests on a SQL Server and this article explains some of the key columns to use in monitoring/troubleshooting.
Here's a link to the first post; sessions and connections and the post contains a link to the next part of the series at the bottom of the page.
Hope you'll find them good reads and as always feedback is more than encouraged, love to know what you think.