First make a note of the name of the file you wish to save. In Mosaic, click on 'File', then 'Web Page Source', then 'File' again, and then 'Save As'. It is suggested that you then save the file on a floppy disk in drive A. This is simpler and you can always transfer it back to the hard disk later on.
You will need to do this for every HTM and TXT file until the entire website is saved. This may be tedious, but once you have made a full copy on a floppy disk, you won't ever have to do it again. You can easily make a second floppy disk copy from the first. You can exit from your web browser, make a copy of the floppy on the hard disk, and use that as your master from now on.
Back in Mosaic, click on 'File' and then 'Open Local File'. Select QUANTUM.HTM as your entry point, and you can then check over the website to see that it is all saved. Anyone else running a web browser on another computer will need to select QUANTUM.HTM as the entry point if they get hold of your floppy disk.
If you are using another web browser, there ought to be an equivalent way of saving a file. Consult your documentation for details.
These instructions are accessible from every HTM file on the website. You follow the same instructions to save a TXT file, although of course the instructions themselves are not immediately accessible.
To save a BAS file, install QBasic as a viewer without the /RUN directive. Within QBasic, where you see the program listing make a note of its name (sometimes QBasic displays the wrong name - use the one indicated at the head of the program). Click on 'File' and then 'Save As' and then save the program as with an HTM or TXT file.
If the floppy disk is run on another computer, then that computer will need QBasic locally available. A BAS program may be run from QBasic without running a web browser, but of course you will not see the HTM file which introduces the program. To run a BAS program within the web browser on another computer, QBasic will need to be present and installed again as a viewer on that computer.
These instructions may be accessed from many different parts of the website.