Once you've opened the CMS, you'll see the Dashboard. To find your page inside CMS:
Note: If you find another page in CMS with the same name as yours, but it's not following the path of the URL of your page, that's not your page! You need to follow the path to get to your real page.
In the current CMS, once you're logged in, you can also browse the live website where you will see a blue BigTree bar at the top of the browser window, allowing you to surf to a page and then choose to edit it directly.
If you don't want to see the blue bar all the time, you can minimize it by clicking the X in the far right of the blue bar (not pictured above). This will minimize the bar to a blue tab showing the BigTree icon. When you find a page you want to edit, just click the BigTree tab to view the whole bar and choose an edit mode.