Viewing the content of files using cat works just fine, if all you want is a quick look at a small file. Larger files can prove to be problematic for cat to handle. That is where less comes in. Less provides you with a more flexible view of files and also allows you to do much much more. For a full tutorial on the usage of less with examples check out this video tutorial.
The cat command which gets its name from the word catenate, has a very basic function that is to take some kind of input file, or input from stdin (the keyboard) and write it somewhere else. This could be to stdout(the screen) or another file. Cat is a very versitile tool and is able to work with any file type, whether it be a text file or a binary file. You can also use cat to view the content of a file right in the terminal window, by simply typing cat and then the name of the file you wish to view. To see cat in action check out this video tutorial on cat usage.