A deductible is the amount you pay out of pocket on a covered claim before your insurance pays the rest. It applies to your own vehicle — collision and comprehensive — not to the liability coverage that pays other people.
Raising your deductible lowers your premium, because you're absorbing more of the first dollars of a claim. Lowering it does the opposite. Neither choice is automatically smarter; the right one depends on what you could write a check for tomorrow without it hurting.
The common mistake is choosing a deductible to hit a monthly payment target, then discovering after a fender bender that the repair costs less than the deductible and the claim isn't worth filing. We'd rather have that conversation before you sign — not in a body shop parking lot.