What are the certifications? Why do I need them to work with you?

The certifications ensure that you understand what is requested of you in every project. They’re small “exams” that test your knowledge for that particular project or language and are very useful as they ensure you’re up to speed when you start working. The instructions of each project will specify which certifications you require.
On top of that, you can take other certifications that will prove your skills in certain areas, like a determined language.
Once you get a certification, it’ll stay in your profile. You won’t have to retake it every time it is required for a different project.