Please forgive me if this sounds like a silly question or two, but I have always drawn tracks on the default‘F.Cu’ layer of the board. This issue is not dealt with in any of the documentation I have read including Getting Started in KiCad.
Assume single-sided PC Board.
When I create a .KICAD_PCB file in PcbNew which surface am a looking at? I have always assumed that I am looking at the top (non-copper) surface on which the detail of the F.SilkS layer will be printed.
If that is correct, then should I now draw the tracks on the B.Cu layer, i.e. on the copper (or bottom) side of the board?
Your assumptions are right, the top part of the board can be considered also the “component side”, if you indeed put your components in the upper part and only have one copper side, then the tracks should be drawn on the bottom layer. However it is just a convention, if you decide to draw your tracks and your silkscreen in the top layers to avoid the mirroring of the information, then the other side will be the “component side”.
You are looking at the component side aka. “Top” or “Front”, although you see all layers that are currently enabled.
Assuming your components are all though-hole components then yes, for a single sided board the tracks and pads should be on the bottom copper layer. It is more than a convention however, tracks on the component side of a single layer through-hole board would be difficult if not impossible to solder nor could it be manufactured by an assembly house since it could not be wave-soldered.
For surface mount components you want your tracks and pads to be on the same side as your surface mount components. If you have a mixture of surface mount and through-hole components then you either need to place your surface mount components on the bottom layer, which adds complexity to the assembly process, or use a double sided board.
And since there is seldom any difference in cost between single sided and double sided boards there is no reason to limit yourself to a single layer board, unless you plan to etch and drill the board yourself.
It depends, on your willingness to work with some text editor (that does not insert strange formatting codes or insists on having some header - I use Notepad++. Don’t even think of using Office…).
Make a backup of your board file (that’s important, please do it.), open it in the editor and work with “search and replace”. Replace F.Cu with B.Cu and save.
If all went well, the traces have changed the layer, if not and you have no idea why, use the backup and start redrawing.
All the other answers are good, but I have a question for you. Are you planning on etching (milling, etc) your own boards, or will you be sending the boards out for fabrication? The layer names are really communication from you to a board house to which layer is which. If you are your own board house you can ignore yourself and build the board the way you actually intended in the beginning. Just watch your mirroring when printing on transparency or toner transfer paper to make sure the toner is directly against the copper layer, instead of on the opposite side of what it is printed on. This should be obvious for toner transfer, but it is also important for nice sharp line edges when using photolithographic techniques.