An
SVG is just any file with a .svg extension.
.svg extensions are used for
vector drawings.
Vector drawings are drawings made out of lines instead of pixels.
You might be familiar with Paint, or Photoshop? If you draw something in Paint or Photoshop you draw pixels (little dots with colour). Vector drawings instead use… well,
vectors. Let's call them lines.
This has a few advantages - you can zoom infinitely in vector drawings, for example, and they are often very small files. This makes vector drawings very well suited for online map games, like Warzone.
Just like you need Paint or Photoshop to make pixel drawings, you need a program to make vector drawings.
Inkscape is a free program in which you can draw with vectors. It has a big community and very good online tutorials (and is free), so it is a good program to start with.
You can download it for free on
https://inkscape.org/ and start making maps!
https://www.warzone.com/wiki/Map_Making has a step-by-step tutorial to make a warzone map. If you follow the steps, you'll have a simple (and probably crappy) map at the end of it, which is a good starter!
https://www.youtube.com/watch?v=iOR9ltkY65s is a good one, too.
I think that's enough to get you started. Once you've read the wiki and downloaded Inkscape, get back to us for more specific questions and we'll help you out :)
