As Eclipse base installation you can use any existing installation you already have or start with a fresh one for Graphiti. Eclipse downloads are available from here, any package listed on this page should do, but we recommend using the Eclipse Classic or Eclipse Modeling Tools packages.
Note: Graphiti 0.7.x runs against Eclipse 3.5 (Ganymede) and Eclipse 3.6 (Helios), while Graphiti 0.8.x will run against Eclipse 3.6 (Helios) and Eclipse 3.7 (Indigo). So keep an eye on these version ranges for your installations.
To actually install Graphiti have a look onto our download page, all available versions and the locations of the update sites are linked there. When you are using an Eclipse Indigo installation (Eclipse 3.7), you don't need to add an extra update site: Graphiti is already available from the preconfigured Indigo update site.
To start, choose the Graphiti SDK Plus feature from the list of available features. It contains the framework, the documentation and the examples including the Graphiti tutorial described in the documentation.
After finishing the installation and restarting Eclipse, choose 'Help' --> 'Help Contents' from the Eclipse main menu and browse for the section on Graphiti ('Graphiti Developer Guide'). Read through the Tutorial introduction and scenario description and start right off with building the tutorial editor. The tutorial is also an excellent starting point for writing your own graphical editor. Simply go through the steps of the tutorial and replace the domain objects and the visualization in the diagram with whatever your usecase requires.
In case of more detailed or further questions how to use the Graphiti framework check-out our forum and/or Bugzilla component; there's quite a bunch of already answered questions there, if yours is not, feel free to open a new topic. See our support page for details on the forum and Bugzilla component.
If you want to change the Graphiti framework itself and start to make contributions you should get familiar with the general Eclipse Development Process.
More Graphiti specific information can be found on our developer resource pages.