Name, class, race, level, handedness, ability scores and proficiencies: set when the character is made.
Drag a panel by its ⠿ grip to move it, and click its title to fold it.
Your DM runs this from the DM Screen. Your turn starts and ends with it.
Tick a box to pin a trait to your character sheet.
Tick a box to pin a feature to your character sheet.
At each Ability Score Improvement level, choose +2 ability score points or a feat. Tick a box to pin a feat to your character sheet.
Click a saving throw to pin it.
Click a skill to pin it.
Tick a box to pin an attack to your character sheet.
Tick a box to pin your armor to your character sheet. Change it in the Inventory tab.
Open a character to track resources.
On your turn, you can do these in any order. The numbers are just for reference. You can also split your movement, for example moving 10 feet, attacking, then moving the rest. Some bonus actions do depend on something else first, such as off-hand attacks, which need the Attack action.
Tick the box next to each spell you have prepared. Checked spells appear under Cast Prepared Spell in the Combat Menu.
Spell lists sourced from the "core" class lists at dnd5e.wikidot.com. Hover details are brief paraphrased summaries, not the original text — use the linked page for full rules text.