How to best use that sheet will vary depending on the character class, and how you like to keep track of things. There isn't any specific rule about what to write on the sheet, as long as it helps you to accurately track what spells your character has prepared at any given time (and for Wizards, what spells they have collected in their spell books).
Clerics don't have to worry about learning spells
For a Cleric (or Druid, or Paladin1) spells "known" means all of them, so there is no need to write them all down unless it makes it easier for you to pick them. A Cleric will use it a bit more like a scratch sheet, writing down or marking whatever spells he has chosen to prepare for the day (including any he gets from his Domain) and changing those if he chooses different spells on a different day.
1 These three classes are called Divine Casters and their magic operates differently from Arcane Casters
Arcane Casters have to learn spells
Wizards "know" the spells they have collected in their book (potentially up to all of them), and prepare a subset of those spells for a given day. So a Wizard will write on the sheet all of the spells he has in his spellbook, and fill in the bubbles on what he has prepared for that day.
For a Sorcerer, Bard, Ranger, Warlock, Eldritch Knight, or Arcane Trickster, spells known and spells prepared are the same; simply write down those few spells he knows, as those are the ones he has prepared always, and those only change when he goes up in level.
The above has nothing to do with spell slots, which are on a table in your character class description, and tell you how many times you can cast, of each level of spell, from whatever spells you have prepared by whatever method your character class prepares spells.