Creating Network Between Macbooks for Screen Sharing
You can create an ad-hoc (computer-to-computer) network which will allow the two computers to talk.  

Click on the Wifi icon in your menubar.
Click Create Network....
Put a Network Name (SSID) in the dialog box, choose a channel.
Click the Create button

On your other computer, join that network like any other Wi-Fi network.

You may be prohibited from creating an ad-hoc network. If so:

Go to System Preferences -&gt; Network -&gt; Wi-Fi. 
Click on the Advanced button, then the Wi-Fi menu item.
Deactivate the checkbox require admin to Create computer-to-computer networks.