In the top left corner, as guest, you will see "Welcome Guest [Log in | Register]
Read the 4 lines/rules that are generic for the entire board and click "I Agree"
Fill out the form, all fields require some entry. Make sure to use the Runescape Name exactly as it is in game, so the forum can pick up your data from the Jagex site.
Don't forget to answer the captcha request (where you have to retype something, so the forum knows you are not a malignant program but a person). Then confirm
If the form comes back with a message you missed something, please fill in the part it misses.
You will get a confirmation that your registration went up for approval.
Then mention you registered to Angie, Christie or Me and we will approve the registration. After that you are a Forum Member.
As Forum Member, you can see all of the Public Forum and a few items in the Members Forum. If you become a Nescio Member, you will be able to see all of the Members Forum - be it not the poll-voting part while you are still a trial member.