I downloaded an eclipse project that has a .classpath which has class entries that need to be updated.
What does this do exactly?
Can I change the content of the .classpath in eclipse?
I opened User Libraries in eclipse expecting it to have the same content as .classpath, but there is nothing in it.

The contents of the .classpath file can be changed by modifying the project Java Build Path parameters.
For instance, in Package Explorer, right-click on the project and select Properties… In the Properties dialog, navigate to Java Build Path in the tree. Usually the Source and Libraries tab panels provide most of the information in the .classpath file.