TP-Link TL-WR703N encryption / password anyone?

So I got this new wireless router...

I connected the LAN cable from the wall to the router, and plugged into power.

I can see the wireless network and connected to it.

The only problem is: HOW DO I ENCRYPT IT???

I want to password-protect this, is there any way? There are ways for Windows XP and 7, but doesn't work for my macbook air.

(Sometimes Apple makes everything way too difficult...)

Does anyone know how to encrypt TP-LINK_blahblah to require a password to connect to it?

Thanks so much!