How 2024 encounter difficulty works
The 2024 rules (SRD 5.2.1) rate a combat encounter with an XP budget. First pick a difficulty: Low, Moderate or High. Next look up the XP Budget per Character for each character's level and add those numbers together; the total is the encounter's budget. Then spend it on monsters, using the XP value in each creature's stat block.
There is no extra multiplier for fighting several creatures, so ten goblins cost exactly ten goblins' worth of XP. A fight inside the Low budget is a warm-up with a scary moment or two, Moderate puts the party in real danger, and High can drop one or more characters. For a party of four level 1 characters, the Low budget is 200 XP.
Fairfight does the adding for you: set party levels, tap monsters from the 341 SRD 5.2.1 stat blocks, and the meter shows which budget the fight fits.