And clarifications or summaries of rules for easy reference.
Spellcasting (summary review from Player's Handbook, etc.) - including this reference for spell modifications.
Classes (Cleric, Fighter, Wizard, etc.)
Actions (Attack, Cast a Spell, Disarm, etc.)
Spells (some are modified - see Spells tab here for "official")
Background (Criminal, Hermit, Soldier, etc.)
and try out "This is your life" (uses a nice system from Xanathar's Guide (p. 61-74) to give some ideas on personality)
and (scroll down to class/race/background - select yours + generate) personality randomizer (repeat until you like)
for: Making a Character / Gear / Playing the Game / Combat / Adventuring Challenges
Sage Advice (authors fix and clarify things) [5E Tools here]