I visit that stage door all the time. if you're standing in front of the building and facing it, you take a left around the corner of the building and continue down until you hit it. When it's not very busy it's a great location, but when it's busy for more popular shows (Waitress, Wicked, etc.) it can be hectic due to the lack of organization. Most actors are happy to stop and sign, but some might walk past unless you ask specifically (the norm for most touring shows). Have fun!