If you want to get the sources of EMF Parsley, for instance, to contribute new features and patches, you can get them via Git and setup the workspace manually. However, we strongly reccomend to use the automatic procedure detailed below.
If you want to develop also the RAP version of EMF Parsley, you will need a different workspace (and a different target platform).
We use Oomph for provisioning a full Eclipse IDE and workspace setup for Parsley.
Press next and finish. This will first create an Eclipse installation with all the needed plug-ins for developing EMF Parsley and then will start the new installed Eclipse (press Finish to close the first installation dialog). The new installed Eclipse will automatically setup the workspace and you will have to wait for this procedure to end (you can click on the animated arrow icon on the status bar to show the progress).