1.) SAVING THROW Target Number. To hit someone with an attack, your die roll and bonuses need to exceed their armor class. Exceeding their armor class is the target. But I haven't figured out what number you are chasing to successfully get a saving throw. I get I am adding my CON, or CHA modifier to my roll, but how is it determined what number I have to hit in the first place? Conversely if I am playing a caster who uses spells that grants savings throw checks to the enemy, is there anything I can do passively or in my build to make it harder for them to hit the checks? What number are they trying to roll to make the saving throw successfully. I have seen active skills and spells that you can use which will impact enemy savings throws but unsure of passive options I can choose or get in a build.
The other questions will have to be answered by someone who's played EA, but I can answer this one.
Saving throws are against the DC of the spell or ability the character is saving against. Typically a spellcasting DC, but some other abilities give saves as well (like some weapon actions that inflict debuffs).
Let's say Gale is casting Fireball - all the creatures in the area need to make Dexterity saves against his spell DC, which is based on Intelligence because he is a Wizard. The ability score that determines a save DC depends on class, and is typically the spellcasting stat for the class (Wisdom for Clerics and Druids, Int for Wizards, Charisma for Bards, Sorcs, and Warlocks). You can improve your chances to hit by buffing your own character's spellcasting stat, or by debuffing the ability that creatures roll to resist it (Dexterity, Constitution, and Wisdom saves are the most common).
Conversely, enemy spellcasters can be debuffed by imposing penalties on their spellcasting stats, or by buffing your party's saving throws.
The saving throw used will vary based on the spell or ability. Fireball uses a Dexterity save, but Stinking Cloud uses Constitution. So the best strategy will depend on the situation.
https://bg3.wiki/wiki/Difficulty_Classhttps://bg3.wiki/wiki/Saving_Throw