Could anyone explain this a little please?
I know I'm asking a lot of questions, however there's nothing on the Portal 2 Mapping Wiki about this item. Which I would like to add to my map.

Hi!

Here are two useful things on the subject:

Mapping Wiki Page:

https://developer.valvesoftware.com/wiki/Prop_portal

http://www.youtube.com/watch?v=OHgJ32wZVJI

Hope those help!

Thanks Tmas :3
Ironically the video tutorial was more helpful than the documentation wiki o.o
now I can use these in my maps >=3