Start with the official basics. Watch the video at the top, read the description, and then watch any of the other videos that might interest you.

Here's a bonus unofficial video about D&D that I find very good for beginners. It's a little long (a little over 24 minutes), so it's not required (but it is very good and will definitely help).

Create a free account and login to D&D Beyond, the official home of D&D on the web. You don't need a paid account. Try to make a character. If you have a campaign link from your DM, click that to start creating the character in your DM's campaign or add your character to the DM's campaign. If you don't want to make a character, you can instead choose from a number of pre-made characters to play here: https://www.dndbeyond.com/characters/premade.

If you're playing with me and you don't want to make a D&D Beyond account, just let me know. We can arrange a paper-based (old-fashioned!) solution for you, or you can still use the pre-made characters above without an account.