Click Edit. After a moment, a Google document editor will be displayed where you can start editing the file.
Collaborators and above can edit any file. Creators can only edit their own file. If you do not see the "Edit" button, you'll need to contact your administrators to request they change your permissions.
When you are happy with your changes, click the Save Changes to Onehub button to update the file in your workspace. If you would like to abandon your edits, click the Discard Changes button instead.