In the Faster Campaigns system, a page can have multiple elements on it. An element can be a donation form, a simple piece of content, a contact us form, and a number of other types. It is important to understand that a Page is not simple one piece of content, but a group of pieces of content.
After logging in, click the "Pages" button on the main menu:
Find the page that you want to edit, and click the "Edit" button on that page:
Now you'll see a preview page, with all of the site elements. Find the element that you want to edit and hover over the gray header and choose "Edit":
Now you'll see the content editing screen. From here you can simply click into the text box and begin typing.
There are many other features available to you on this screen, including formatting options, images, tables and others. For details on how to use these features, you can read the Text Editor Quick Reference Guide.