The program works only with text file formats. If you see unreadable characters on the screen, then either you have opened a non-text file, or do not have chosen the correct character encoding. Auto-detection of encoding works only for files that support such feature. For all other files, you must specify the appropriate code page.
You can flip through pages of the text by tapping the top or bottom of the screen. Text position is adjusted by pressing in the middle of the screen.
To remove some items from the history list, you can use a long press on the corresponding element.
Use volume keys to adjust the brightness of the screen.