Well, it's easy, just scroll the list and click on folders and files to open them, right? Clicking on the file either opens the file, or opens the context menu, depending on the settings. Clicking on the folder opens the folder. If you click an archive which is supported by the application, it will be opened just like a folder. You can read more in the section on working with archives.
The Back button of your device returns you to the previously visited folder (if there are any), the position in the list will be saved so you won't have to scroll all the way to the selected element.
The Up button at the button panel gets you up the file system hierarchy. The position in the list in this case will always be at the top.
The Home button gets you to the home folder, which is by default external storage. If you go to the settings, you can choose your home folder.
You can sort the files if you select the corresponding item in the menu or in the action bar (depending on your device). Right now the sorting options include by name, by size, by the last modification date, and by type.
Operations with files
To do something with the file, you first have to select it. You can open the context menu by long-clicking the file, or enter the selection mode by clicking the Select button in the panel.