Protection From Evil provides a magical barrier around the recipient at a distance of one foot. The barrier moves with the recipient and has two major effects: First, all attacks made by evil or evilly enchanted creatures against the protected creature receive a penalty of -2 to each attack roll. Second, the protected creature makes all saving throws against attacks from such opponents with a -2 bonus.
A third benefit is not part of the status effect itself, but of the various Protection From Evil spells instead: Summoned demons cannot target the protected creature.
If the caster is evil-aligned and protected from evil, they do get save bonuses against their own attacks.