Use DnDBeyond to create your character.
Use the Player's Handbook (PHB), Xanathar's Guide to Everything (XGtE), and Tasha's Cauldron of Everything (TCoE), Tome of Heroes (Misgard), or Deep Magic (Midgard)
Anything in the PHB or XGtE that isn't listed as Variant or Optional, is legal unless this document says otherwise. Ask if you're not sure.
Some races might have social consequences (e.g. Half-Orcs) but just like you'd expect in real-life. E.g. intolerant jerks
Some classes might have social consequences (e.g. necromancer).
Multiple players can play the same class but let's try to keep the number of identical sub-classes to 2.
Generate Ability scores using the point buy or the standard set.
Alignment: Pick a non-evil alignment, the exact one won't matter that much in-game.
Variant or custom Backgrounds are okay.
The Retainers variant feature of the Noble/Knight background isn't allowed.
Feats from the PHB and XGtE are allowed.
Starting equipment: Buy and sell your starting equipment as needed before the first session
New players (not characters) might be able to start with additional equipment. Ask the DM for details.
Bonds: Add one from D&D Beyond and then add two custom bonds that are directly related to other PCs so there's some party connection.
Start with a basic backstory. The best backstory is one created at the table, not at the writing desk.
Ideas.
You'll need a token for your character. Circle is best.
Build a solid character if you want, but don't try to min/max everything or exploit the rules.
(Optional) I highly recommend Live to Tell the Tale ($10) to better understand D&D archtypes and combat. It's the best resource I've seen on character tactics and can make the combat side much easier and more fun.