A car refinance loan is one in which a new lender will loan you money to pay off your original car loan. You then pay off the new loan over time. It makes sense to do this if loan interest rates have fallen and you currently have a high-interest car loan.
Any lending institution will help you, such as banks, credit unions, etc. and there are numerous websites offering to refinance your car. If you want to pay less interest over the life of the loan, then keep it for a short term. If you want to lower your monthly payments, then lengthen the term of the loan.