Depends on the time of year you go. They sometimes take reservations, but most of the time, they don't.
It's on a "first come first served" basis. Around the main eating times, the wait can get rather lengthy, but if you go for a late lunch or early dinner, you can most likely walk in... Depending on when you go.
If you're going on or around the 4th of July, it will be packed and they don't offer a lot of their regular menu like appetizers. This gets you in and out faster so more people can come in and spend more!
Have fun.