There are number of ways you can contribute and support the project.
Traccar project contains server side part, web interface and mobile apps. You are welcome to contribute code to any of those projects. We have a high level architecture documentation and the source code is very clean and pleasant to work with.
Translations are important to many people who don't know English well enough or prefer interface their native language. If you want to contribute to the project localization, you can do it through the Transifex project.
If you are a happy user of Traccar software, let other people know about the project. Also, follow the Traccar community on Twitter and Facebook.
If you don't have time or skills to contribute to the project but you want to help our open source project, you can also support it by donating.