dnd 5e – Capacity check vs dc backup

In D & D 5e, wizard spells may require a check of their abilities against saving spells in time.
THIS IS NOT ON THE CALCULATION OF THE SSDC!
If the spell says that a creature can see through the effect if it passes an Int against an SSDC, how does it work? A d20 is cast by DM and the mod Int (if any) of the creature is added and must be beating (being greater than [or equal to?]) the SSDC of my assistant (8 + Wis mod + Prof)?
Thank you for any confirmation or education on this subject.