In his short on C style in week 1, Tommy refers to a style guide. I can't find it. Where is it? I have already looked through the cs50 site and can't find such a document there.
Styles are important because they specify good coding habits, which gives you comfort when working in a team, as everyone would be following the same convention, so it will be easier for others to read your code( and vice versa).
CS50 has a online Style Guide that has a good description to stylize comments, conditions, switches, functions, indentation, loops, pointers, and variables. You might also be interested in Style Conventions and Coding Conventions.