Shuttle buses are provided at most of the airports by the car companies. They shuttle back and forth between the airport and the car rental company picking up and dropping off passengers. When you receive your confirmation email from us, click on the SEE DETAILS link, and read the instructions. The details for the shuttle should be located there along with a lot of other valuable information.
Some off-airport locations will provide shuttle pick up at hotels etc. You will have to read the SEE DETAILS link to find out if your car rental provides this service.