There are several ways to contribute to the project. If you are a PHP developer you should connect to the developer forum. There you can exchange with other developers. We are hosting the friendica core and the addons at github. So you need to create an account there.
If you want to help with the translation in other languages, please have look at Transifex. You need a account there and provide an easy interface to translate. If you do not want to deal with development tools like git that is fine, we will take care, that your work will be included into the project. More information about the translation process can be found here.