Welcome to the forum.
You were accepted to sign up for the forum. Nearly any human being is accepted. We don't like bots and spammers. Real people that are interested in long distance motorcycle riding are welcome. (Excepted means to exclude. Accepted is to approve or recognize.)
You will be assigned a membership number only after you join the Iron Butt Association by completing one of the rides listed
HERE. For a variety of reasons, it is strongly recommended that you do one of the basic entry level rides, a Saddle Sore 1000, (1000 miles in 24 hours), or a Bun Burner 1500, (1500 miles in 36 hours), and submit the documentation for that ride for verification by the IBA. Each of the rides listed has a link to methods of documentation required and how to submit that to the IBA.
There is more than one method, so take the time to read and understand them and choose what works best for you. Ask questions on this forum if you have them. It can take several months for your first ride to be verified and a number be issued to you. You don't need to wait to do more rides, as there is no time limit for rides being submitted as long as you still have all the documentation. Typically people wait until they have a IBA membership number before submitting another ride, but it's not required. You simply need to make a note on other submissions that you are still waiting for your first ride to be verified. This avoids the accidental issue of more than one number.
It is suggested that you start out with a SS1K or BB1500 so that you can better understand the differences between riding/planning a trip at your own pace and riding/planning/documenting an endurance ride of 1000 miles or more, and to practice the methods of documentation. It would really suck to do an epic multi-day ride, only to realize later that you missed important steps to document it to the IBA's standards.
Please read though
This Page, as many find the information helpful. Some of it you most likely already know, but we don't know what you know, so offer the helpful info to anyone.
The home page for the Iron Butt Association has many other links to useful topics and a FAQ. You can find that here:
https://www.ironbutt.org/