Hello,
you have two options:
1.) Download jbpm-5.x.y.Final-installer-full. This way you receive whole jBPM suite with correctly preconfigured Eclipse. You do not have to care about configuring Eclipse.
2.) Download just jbpm-5.x.y.Final-bin file. In your Eclipse go to Window -> Preferences -> jBPM -> Installed jBPM Runtimes and add a new runtime with a path which leads to your downloaded folder. Check build paths of your projects if there is your jBPM library added.