If you are one of the people that said what the title of this journal say then read further and get it inside your head OR Bookmark this page and read it when you find yourself starring at a file on your desktop!
I've been there, not knowing what to do with a file. The answers are right in front of you, all of them are waiting on Google. Learn to use the internet people :)
The following short file descriptions means:
.ai --> this is an Adobe Illustrator file
.psd --> this is an Adobe Photoshop file
.abr --> this is an Adobe Photoshop BRUSH file
.csh --> this is an Adobe Photoshop SHAPE file
Now, when you read somewhere CLICK TO DOWNLOA