Optics question

My wife and I were having trouble with how Optics works, the “add +1 die modifier,” would that add an extra die to the roll or would it add one to the roll result ex. a roll of 2 is counted as a 3 and therefore a successful hit with the deadeye? We come from playing 40k where some abilities or effects can modify the roll result so we werent sure. Thematically it makes sense that having an optic on a gun would make it shoot better, not shoot more, ya know?

If it DOES modify the roll result, would an item like explosive ammo stack the roll result modification from optics? If not disregard

My wife and I were having trouble with how Optics works, the “add +1 die modifier,” would that add an extra die to the roll or would it add one to the roll result ex. a roll of 2 is counted as a 3 and therefore a successful hit with the deadeye? We come from playing 40k where some abilities or effects can modify the roll result so we werent sure. Thematically it makes sense that having an optic on a gun would make it shoot better, not shoot more, ya know?

If it DOES modify the roll result, would an item like explosive ammo stack the roll result modification from optics? If not disregard