Plugins are Python scripts and are usually distributed in source form as .py files but the can also be distributed as compiled .pyc files.
The plugin files are placed in the
Plugins directory where Graph is installed, and will automatically be found and loaded by Graph.
Plugins are scripts, which are just small programs that run inside Graph and interacts with Graph. But a plugin can do anything that a program with the same rights can do. This means that if Graph is run with administrator rights, it is possible to write a plugin that erases the whole hard disk. Therefore you should be careful about which plugins you use and only install plugins from a trusted source, or at least you should check the source code for suspicious parts.