Thanks to @HeatherWaite8 for this art piece!

At level four, nearly every class eschews getting a class-based improvement and grants the player the ability to choose whether to take a Feat or gain an Ability Score Improvement (ASI). The only two exceptions are druids and monks, who also get a class-based improvement (Wild Shape Improvement and Slow Fall, respectively). Most of the primary spellcasters (bards, clerics, druids, sorcerers, and wizards) also receive an additional cantrip and an extra second level spell slot per day. Warlocks just get the extra cantrip, but they, like bards and sorcerers, add one spell to their known spell list in addition to the cantrip.

If the player chooses to go the ASI route, they can choose to either give themselves a permanent +2 to one of their ability scores (Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma) or a permanent +1 to two of their ability scores.

If the player chooses to go the Feat route, they can choose one of the Feats listed in the D&D handbooks, like the Player’s Handbook and Xanathar’s Guide to Everything. Sometimes these feats give the character specialized abilities, sometimes it allows the player to increase one or more abilities or skills (like athletics or passive perception), and sometimes they do both. Some Feats can be achieved by anyone, while some have race, spellcasting, or ability score prerequisites. For example, Prodigy (which Beau took as part of her variant human traits) can only be taken by humans, half-orcs, and half-elves.