JPEG- a JPG is a simple and most used image file which will be used for social networking, web design, and graphics.
Gif- a Gif file is another image file but uses certain amount a frames to create a short animated image, also used for social networking and web design.
PSD- Is one of the first all round file that be used for Images,Video,Text ect. Made as an early translator for other new programs being released.
PNG- 'Portable Network Graphic' file was made to be a replacement for a Gif file since it does same stuff with the exception of being able to be edited and compresed for the Internet.
Tiff- 'Tagged Image File Format' is another image file but far more complicated, for use of proffesional graphic designers and proffesional Photographers with some amateurs as well.
Finally a 'File Extention' or 'Filename Extention' is way to change a file from being 'example' a PNG to a JPEG, by adding '.png' or '.jpeg' at the end of the file. This won't change the data of the file but allow you to access it in another program, however you can't change a text file into a image file and expect a Program that deals with images to be able to open the file.
