How to modify classpath in Eclipse?

Again, I saw this sentence:

A .classpath file snippet that can be included in your project's .classpath has been provided here(ie, a link). Please only use the classpathentry's you actually need (see below for details).

What do these sentences mean and how can I add that code snippet to my classpath file in eclipse ?

Please help.

What is classpath in Eclipse project?

classpath maintains the project's source and target references for Java compilation and compressed file or project dependencies. This configuration is maintained through the Java Build Path page in the project's properties.

I understand this as you want to find the classpath file. Go to eclipse and press CTRL+SHIFT+R. Type .classpath and select the file in your project.

Note: If you're modifying this file and you don't know what it is, I advise you be extra careful :).