From the dashboard, choose a plan. Click the files tab to get to the file browser. Click on a folder name to change to that folder.
The current folder/directory path is shown across the top, like:
Back to: home > folder1 > folder2
You can click on any of the folder names in this folder/directory path to jump right to that folder.
Click on a file to open or save it. You can “edit” a file by saving it to your computer, editing it, then uploading it back to the server (see Uploading a file for more info).