Welcome, and first of all, thank you for wanting to help out.
Spinel is a big project, and therefore, help is welcomed and encouraged. You can contribute in many different ways, which are listed below.
Providing feedback and reporting issues in the code should be done using the issue section. Please file in a new issue following one of the available templates.
You just made an awesome improvement to the engine and want it to be featured ? Open a pull request and add @l3alr0g to the reviewers. Opening an issue before making any changes might be a good idea in order to clarify what your goal is precisely.