Throughout this site, the term "track" refers to a "line" of copper on a printed circuit board. It is how devices soldered to the board are interconnected.
Sometimes an alternative term will appear, if not here, then certainly in other people's documentation: "trace". Tracks and traces are the same thing, in this context.
In simple single sided boards, all of the tracks are on what KiCad and most PCB design packages and designers call the "back" or "bottom" "layer" of the board.
Most of the time that you are working on the board, you will be working on it as seen from the front, with "X-ray" vision. If you are making the actual physical board by hand, when you print the artwork, you tick the "mirror" box in the "print" options so that the hardcopy will show you want the tracks look like as seen from the "back" side of the board. (Without "X-ray vision"!)
(Vers 4-0-4): The basic PcbNew would draw all tracks at the same width. If, from the menu bar, you go into "Design Rules/ Design Rules (yes: again!)" And select the "Global Design Rules" tab, you will find a table "Custom Track Widths". Add or more entries, to add strings to your bow. When you've done this, you can change the current track size "in your pen" with a box on the top tool bar, left hand end.
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