When you start TPU, it looks for a file with the name you give in the command. If the file is there, the highest version of it is read into the upper window. If the file is not found, a message appears in the lower window, and the End of Text line appears in the upper window. Type in the words you want in your file, using the typewriter keyboard. You can move around in the file using the arrow keys.
Most files are longer than one screenful of text.
If you want to see the beginning, use the arrow keys and move up. As you move up, the last part of the text will scroll off the bottom of the screen, but it is not lost. Closing the edit session and saving the file CTRL-Z closes the edit session and saves the file. TPU can do much more than this, but you can create and change files adequately knowing only this much.