To join as an Ordinary Member you first need to register as a User and then click on the Large Button that will take you to the Membershipo Application Page.
If you have been a User for some time, then click on your name (top left) and you will see 'Profile'. Click on Profile and you will see the link that takes you to the Membership Application Page
Membership has a small annual subscription of £10 for adults. Junior Members are Free.