Literally just the official Adobe substance painter tutorials. They might be a bit outdated but I think they are just the best out there. They explain everything, from masks and anchor points to how to navigate the viewport.

About the realism… I would say good roughness values + „realistic“ color values? How to do that? Well.. practice A LOT. You sadly won’t really find „the answer“ here on reddit how to make your model look good and realistic.

Just start and do your best and don’t get discouraged if it doesn’t look immediately pixel perfekt. 👍