People allowed to edit the website will have one or both of the following roles:
The former can access and edit pages, stories etc., whereas the latter have more comprehensive facilities to administer more of the Drupal system. It is expected that new users will be given the contributor role only.
Note: There are additional levels of administration that the webmasters have.
The user log in page is user.
When you complete logging in the navigation menu on the left changes to include an Admin section, if you're authorised to access it, Forums and a Log Out entry at the bottom of the first block. Most people will never need to go to the Admin section unless you are creating some new content, e.g. a new Page or Story.
Whenever you go to a page on the site the top of the page/story, immediately under the header, will have View and Edit buttons (possibly some others for different Drupal features). Click on the Edit button to change the page/story.
If the View and Edit boxes don't appear on the screen when you try and access the britgo.org page you're interested in, then go to the login page and enter your user name and password. You will stay logged in until your browser window closes or you deliberately Log Out.