The below will export and import both apps and adapters belonging to the same project.
Export - In Eclipse, right-click a project and choose Export... choose to export the project as a zip file. Import - In Eclipse, right-click the Project Explorer view and choose Import... choose to import an existing project (your zip file).
An app is contained in the appName folder within the apps folder. And adapter is contained in the adapterName folder within the adapters folder.
There are no mechanisms to export and import the CODE of an adapter or application. You will need to copy-paste the files/folders manually and likely change many references in your files as many locations have different values based on the project name you've used.
Such an approach is highly not recommend by Worklight.
Starting Worklight 6.1, the training modules also contain a portion about how to import projects.