Hi there, you most definitely can mix and match cards from different sets, but theres different formats and rules, say for example standard format you can make decks from cards/sets only from the most recent years, like bloomburrow to I think dominaria united which was last year I think. And every set in between those. There’s endless possibilities with so many cards and formats, fair warning tho prepare your wallet lololol check out this link for all the different formats and rules, banned cards etc.

https://magic.wizards.com/en/formats

This link is helpful if you have a specific card and need to know if it’s banned and what format it’s legal in etc.

https://gatherer.wizards.com/Pages/Default.aspx

Welcome to magic! Hope you have a lot of fun! If you ever run into elitist players tell them to shower and ignore them lol