This should cover the (very) basics well:
If you want a video, something like this should cover the bare-bones basics:
Once you have a sense of the basics, the best way to learn is to play and look up rulings whenever you get stuck.
Basic official rules are here: https://magic.wizards.com/en/magic-gameplay
Comprehensive rules for the current season are here: https://media.wizards.com/2019/downloads/MagicCompRules%2020...
Whenever there is a ruling specific to a card and its non-trivial interactions, you can look the card up in Gatherer, and there will be a rulings section that will tell you the relevant info. For example, if you were using the card 'Felidar Guardian' and didn't know what would happen in a particular case, you'd look up its Gatherer page: https://gatherer.wizards.com/Pages/Card/Details.aspx?multive...