oh, ok. Perfect example of how the wording of this stuff is confusing to us newbies! I think im starting to grasp it all then.
So weird that they dont just call it spell attack then? Considering its not added in any way to the defensive roll.
But I guess that one isnt on Larian

Edit: originally i thought I as the attacker rolled the 1d20 + my modifiers vs their spell save dc + modifiers. I guess the wording made it seem like spell save dc was like armorclass but for spells.
Yup yup, spell save DC (difficulty class) is kind of the inverse of AC (armor class). Stated more concisely than my previous post:
For Saving Throw Spells, the attacker rolls nothing. Instead, the defender rolls 1d20+modifiers against the attacker's spell save DC, where the spell specifies which modifiers the defender uses. The attacker's spell save DC is almost always calculated using their main spellcasting ability.
For attack-roll-spells, the defender rolls nothing. Instead, the attacker rolls 1d20+modifiers against the defender's AC, similar to weapon attacks. The modifier used is ~always the spellcaster's main spellcasting ability.