How do I join an AI training task as a beginner?

You don't join a task directly. You apply to a role on a platform, get accepted, and the tasks come after that. Each posting has an Apply button that takes you to the platform's own application.

For your background, the postings show these are expert roles, not beginner ones. The maritime one asks for 7+ years of marine cargo and draft surveying plus a Certificate of Competency or maritime academy certification. The mechanical engineering ones ask for a degree and design or analysis experience. The work is things like reviewing photos and documents and writing a short report, or writing questions and grading AI answers against standards.

So your years in maritime and oil operations are what you apply with. If a role asks for something you don't have (for example the U.S. DoD roles), skip it. Whether you're accepted is decided by the platform, and I can't promise it.

Since you're in the UAE, check the side-work rules if you have an employer.