After you log in, you have two ways of getting to the content you wish to edit.
If the content you wish to edit is published and 'live' on your site
Simply go to that page on your website. Click the Edit tab, and you will see the edit screen where you can change the title, content and other settings.
If the content you want to edit is unpublished
You must access it via the content list, found in the Admin Menu as Content Management/Content. The list will provide you a direct link to edit the content.