OK, well, this can be a wonderful experience -- or not. The "or not" is why you need to read up and be prepared, have a vet who will come quickly if needed. Hopefully you will have a mare who, as most do, have no problems foaling.
Go to the "Best of the Forum" area and you will see some subjects about foaling.
Read Blessed are the Broodmares, excellent book.
Prepare a great area for her to foal and you to stay awake many, many nights waiting.
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Take a phone and camera to the barn when foaling time arrives.
Because there is just so much to say -- I'd suggest the forum area of great tips to be read, then hit us with specific questions. Beyond that, I wish you great success and a beautiful foal.
I'm assuming you have "done" your homework on the stallion/mare backgrounds and feel comfortable with the choices and that the mare is fully matured and ready to breed.
I see you are new on the forum, so tell us your background with horses & minis. We may be able to reply with more informative & helpful info, once we've gotten to know you a little more.