The strike is the deductible: losses below it are covered. The premium is the cost of insurance, paid whether or not you use it. Puts are typically bought before events or when a holding is large relative to the account.
A protective put is a pure hedge. Combining it with a covered-call to offset the cost is a collar.
Example: 100 shares at $100. Buy the $90 put for $2.50 with 60 days to expiration. Worst case over that window is $90 - $2.50 = $87.50 per share, a 12.5% maximum loss.
Related: hedge, collar, put-option, covered-call