Mac authentication lets you specify mac addresses which will not go through the splash page and can be automatically use the internet for free. Only local MAC authentication is supported.
Here is how to set up local macauth (so those mac addresses will skip the splash page and access is automatically):
Go to IP > Hospot > IP Bindings.
Add Mac Address: xx:xx:xx:xx:xx:xx
Address:0.0.0.0 Address to:(leave Blank)