select your project, right click to select “Import…”
select an import source: “File System”
Browse your JAR folder
click “enable” your jar and press “finish” button.
select your project and right click to select “Properties”
select “Java Build Path”, and “Libraries” , and “Add JARs…”
pick your .jar on your project, press “OK”
here has a nice video demo to show how to add jars.
http://www.screencastcentral.com/public/yt3334.cfm