In many languages, the type of case we use matters. For example: eCho and echo, could mean two different things. In PHP, commands are not case-sensitive. This makes coding easy, but I personally like to standardize on using all lower case, when working on projects.
On the other hand, variable names, are case sensitive. If you define a variable named num and call it Num, you are going to get a syntax error. In the two videos below, we explore case sensitivity in PHP.