Ratings are qualifications that are added to a pilot certificate.

You must have a pilot certificate first.

You can get an endorsement; for a tailwheel airpalne, for example, when you are learning to fly. It's fine if you're learning to fly in an airplane with a tailwheel, but your focus when learning to fly should be upon the basics. You can pursue various qualifications after you've learned the basics, to broaden your understanding and experience.

The learning you do in your primary training is among the most critical you'll experience in your flying; learn it properly and learn it well.

An instrument rating would do very little good if you didn't know how to fly to begin with.