I am trying train my golden to mark. What is the most common method for teaching this? She holds fine while I throw multiple bumpers, but she doesn't bring them back one at a time and she will go to the second one I throw first, pick it up, then go to the first bumper i threw and she gets confused about what to do.

She's not confused you are...

Dogs will always pick up the last bumper or bird down. It's the last one they see thrown.

Angie

Are you saying she will go pick up the bumper then go to the other bumper thrown without bringing back the first bumber? Therefore she is confused that she cant bring back two bumpers?

I am not a pro but I think this is a good way to start with doubles...

Try either throwing a bumper out letting her mark it then turn 180 degrees and throw the other. Send her for the last one down then when she returns send her for the other.

You can also do this on the corner of a fence or house. One throw down one side the other down the other side.

With enough time you can begin to tighten your marks.

Is she doing singles fine?

After singles are down you start the doubles thrown close to 180 degrees apart so that the dog comes back to you before getting the second bumper, and as Angie said always send her for the last thrown mark first.