Area Portal WTF
Much better explanation: https://developer.valvesoftware.com/wiki/Areaportal
I highly recommend reading that page before trying to use this in your maps as you'll have a better idea about what they do, how they work, and how to use them effectively.
It is used for optimization of your map. Optmization is the process of making your map run smoother.
In order to properly use them you need to have a proper understanding of optimization.
That link is only the section on areaportals but do be sure to read the rest of the guide! It was written for HL2 mapping but 90% of the stuff in it is pertinent to Portal 2 mapping.
http://fc07.deviantart.net/fs70/f/2013/ ... 5s6j19.jpg
I love posting this picture
ChickenMobile wrote:
http://fc07.deviantart.net/fs70/f/2013/020/a/3/leafcomic_by_chickenmobile-d5s6j19.jpgI love posting this picture
We all do 
ChickenMobile wrote:
http://fc07.deviantart.net/fs70/f/2013/020/a/3/leafcomic_by_chickenmobile-d5s6j19.jpgI love posting this picture
LOL haha Does my ass look big LOL! Thaanks for the comic it really helps me understand 