File | Save As
This allows you to save the data displayed in the grid as a Markbook90 file. (Details of its format are described in the technical information). A standard Windows Save dialogue box is displayed.
If you click on [Cancel] (or press [Esc]) then the box will disappear and no action will be taken. If you click on [Save], then the data will be saved. You may find it convenient to use a file extension of .mbk, but this is entirely your choice. The system does not require .mbk, or indeed any extension - it would just allow you to categorise your files.
If the filename you have specified already exists, you are given the option to try again with a different filename, or overwrite the existing file (which will not be recoverable).