using external JARs in Eclipse

In order to use external JAR files in Eclipse, the most robust way if
you develop on multiple platforms is to use "Preferences > Java > Build
Path > Classpath Variables" to add a classpath variable. You can give it
any name you wish, and you must associate to it the file name of the JAR
that you want to include.

import source code in eclipse

To import existing source code in Eclipse, do the following:
1) Create a new project and give it the same name with the directory
containing your source code.
2) Uncheck "Use default location" and manually set the location to the
directory containing the source code.
Usually Eclipse automatically detects your source code, and you can
simply click "Finish" to finalize project creation.