You’re not supposed to hold down the keys. If you hold them down, it brings up Siri, if you just press, it brings up Spotlight (you can hold command as long as you want, just press space). If you have issue not holding down keys, you can disable the Siri thing or change it to a different shortcut.
Not much to learn about Spotlight. It can do a lot, but it’s pretty basic.
Search for anything, and it’ll search content and titles alike to find anything on your Mac or the web. Can be files, word definitions, whatever.
Input a math calculation and you‘ll get the result, like sin(sqrt(3*2)) would be sine of the square root of 3*2.
Input a conversion and get the result, like $50 in Yen and you’ll get 5.404 Japanese Yen as a result.
Or write a stock title, like AAPL, and get a nice graph and overview of the stock.
That’s just a small set of examples. You can input most things in Spotlight. Sometimes it’s a bit like a text based Siri as well.
But it’s not really that big of a learning experience. Want info, ask Spotlight.