If you have never played D&D, the best way to learn what it's about is to watch a game. Check out this 45 minute game with Steven Colbert
For new players, for the first session we will have some characters ready for you to run. You will pick your class (Fighter, Wizard, etc) and your ancestry (Dwarf, Elf, Human, etc) then you will come up with your character's name and personality.
You can dive into the rules by looking at the free Basic Rules and fill out a character sheet
After your first session, you will be expected to take ownership of your character. You can access our campaign on DndBeyond as which will give you access to more resources and tools to manage your character.
If you like a physical book, the first one to get is the Players Handbook, currently $28 on amazon.