Will additional car payments reduce cost of borrowing?

I had 2 auto loans, a car and a motorcycle, and recently received a significant pay bump. I paid off my bike in full less than a year from the time of financing but the car has about 36,000 remaining on it. I don't have the funds to pay it outright but want to make extra payments.

If I send an extra biweekly payment to the loan account, does that go straight to the principal? And if so, does that reduce my cost of borrowing over the life of the loan, or is that locked in at the time of financing? Thanks for your help!