Two questions on Creating A Horse
What exactly goes in the Profile URL section?
Assuming that the Horse Avatar and Profile URL are indeed not the same.
Also, is the birth month of the horse supposed to be the date it was created?
On the main site you have to create a horse, name, breed, color, gene. You have to upload a photo of your horse and that is the avatar for your horse. A number is created and that is the number you will use to register your horse. The birthday of your horse is when it was made so a horse made today would have a 08/2017 birthday. I hope that helps. You choose the size of your horse, so a pony would be like 14.0 hh and if it is a bay the gene would be Ee Aa or chestnut would be ee aa and so on.
The Profile URL is a link to your stable's website, if you have one. A while back many more people ran websites, today the play style has changed and most people just leave that field blank.
Your horse's birthday isn't taken into account as much either. Most people here age their horses 1 year per real-life month until they are 4, then age one year every four months. This isn't a rule, so you can use any aging system you want. I use 3 months = 1 year, so for example a horse with a 01/16 birthday is 9 years old.
I have an age calculator in my gizmos page - check my signature!