What is the garage door made of right now ?

I believe it is white fiberglass or steel with a woodgrain embossed finish. It's about 5 years old and in very good shape. I've been doing a lot of research online and see that there's a number of different ways of doing this. I have done some interior doors by painting a base coat of gold, caramelly color and then applying a brown glaze which I dry brush off. They came out great. I'm wondering if (because it's outdoors) I should apply some kind of primer and off course exterior paint? And also what kind of sealer would be best to finish with?

Have done interiors but not exterior doors. I would guess that you need to use exterior paints and then some type of topcoat or it will wash off over time.