This is something you can accomplish fairly easily.
First, add a few cars to your inventory and make sure you fill out the Make field.
Let's say one of the makes is 'Buick'. After adding the vehicles you can go to http://yoursite.com/make/buick and it will list all vehicles that have 'Buick' in the make field.
There is also an easy way to add makes to your menu. Go to the admin area and click on 'Appearance' then select 'Menus'. In the upper right hand corner of the page you will see a button that says 'Screen Options', click this and a menu will drop down that allows you to add a variety of selections to the page, one of them is 'Make'. If you check the box next to it it will add a section to the page that will allow you to add menu links to specific makes.
I hope this information will help you along and didn't confuse things further. If you need any more assistance on this let me know.