Welcome!
You may use the following shell commands to get the lastest code.
git clone https://github.com/AOSC-Dev/ciel
git submodule update --init
If you want to make changes to anything in /src/ciel-driver, it is at repository https://github.com/AOSC-Dev/ciel-driver.
Plugins are placed at /plugin, this directory will be copied to /usr/libexec/ciel-plugin when you do make install.
You MUST keep the plugin executable, chmod a+x ciel-myplugin.
A plugin could be a shell script, a python script, a binary...
Use ./format.sh to format your code BEFORE committing, I would suggest you to make a symbol link at /.git/hook/pre_commit to format.sh.
Keep it simple and readable. Come on, you can do it right.
But, again, don't forget to use ./format.sh after coding things. :)
about_something: do what
or
about_something: do what; fix #123
You may check the git log --oneline out, there will be many examples for you.