To add or edit content on a Drupal site, usually you have to first be registered as a user.

Llook for a small form called “User login” in the left column of the site. Click the link that says "Create new account".

To register, enter a user name of your choice and an email address to which you have access, plus your union membership information and hit "submit". Then check your email account. Within a few minutes, you should get an automatically-generated email confirming your registration and giving you an initial password to use. Now you're ready to log in.