Comments

Comments are a way of inserting text into UnrealScript code to remind yourself of what the code is doing, or to give a summary of the code file. Comments will be ignored by the compiler, so they can also be used to temporarily 'disable' a line of text.

UnrealScript supports two kind of comments a single comment and a multiple line comment.
single line comments are used like this

// The commented declaration would also make the compiler ignore the declaration therefor it can be useful to disable declarations 
// for various reasons such as testing and debugging.
//var int TestVar;

and multiple line comments are used like this.

/**
 * NOTE: Never change the value of this variable to -1! the class functions always expect it to be a positive-only value!.
 */
var int TestVar;

Because the UnrealScript language commenting style is very similar to other programming languages commenting styles, the following link might be useful
Wikipedia Comment.