Any contribution is welcome. If you would like to fix a bug or add a feature, you can do it ! However, it is important to follow some guidelines so that everything can go smoothly.
If you have an idea or a bug, please report it first in the Issues tab of the repository so we can discuss it and decide of the best strategy to bring your idea to life. Directly issuing a pull request is generally a bad idea: you might end up coding something that has already been done or is being done.
In order to be able to play with this project, you need to setup quite a few things. A very comprehensive and complete tutorial is available here
Once your have setup the project, you can have a look at the Contribution tutorials
An updated version of the documentation is hosted here. This contains details about of each function should work and how to use them properly.