MachinaCraft is a framework for machines made up out of blocks, activated by right-clicking on a lever. On its own it does nothing, but other plugins can use it to let players build a Machina that they can activate.
General information about the plugin, comments page and issue tracker can be found at the BukkitDev project page.
You'll need some knowledge of how to create a bukkit plugin with Eclipse. If you're new to plugin writing, the Bukkit wiki has a tutorial that's a good starting point.
If you've downloaded the project as a zip, do the following:
File -> Import... -> General -> Existing Projects into Workspace
If you're getting the source from Github:
File -> Import -> Git -> Projects from Git
Once you've imported the project, create a new Java project and select the MachinaCore folder inside your project folder. Don't forget to add your bukkit.jar to the build path.
Repeat this process for each plugin folder you want to work on, and also add the MachinaCore project to the build path for sub-plugins.
Eclipse should automatically compile each plugin when it's imported.
A rudimentary ant build system is included that can take care of packaging the plugins into jarfiles. In the MachinaCraft project, rightclick on build.xml and select Run As -> Ant Build (without the ...)
The jar files will appear in a 'jar' folder under the MachinaCraft root folder. Advanced: Create a new builder for the MachinaCraft project under properties so that you can just select the project and in the top menu choose Project -> Build Project.
When you've created a new java plugin project, make sure you add MachinaCore to the build path. For an example on how to make a working Machina plugin you can look at the source code for the existing plugins.