Edit Read loads the file you specify from disk and puts it in buffer 0 aka the cut buffer aka the system clipboard. From there the file can then be pasted into any grid that accepts text from the system clipboard, even other applications.
Edit Write creates a disk file with the name you specify and saves the text contents of buffer 0 aka cut buffer aka system clipboard, into that file. If a disk file of the specified name already exists, its old contents are lost.
Edit Abandon abandons all changes made to the function currently displayed in the main text area since it most recently displayed.