First, you draw just like with ordinary pencils:
Then, time to apply water. The only water available around was £1.50 bottled still water. Meh.
Finally when in the bus already, I have erased some of pencil strokes and added few with a ballpoint pen:
As a result, I am not fully satisfied. First, special technique must be developed when sketching for strokes not to appear through degraded colour later (or to appear, but where is needed). Second, colours are hard to blend and shading the same object with different pencils doesn't help much. Hence, if what you are sketching fits your pencils set everything is okay, otherwise you're in trouble.
Still they are much easier to carry around and to use on the streets than watercolours and when used smartly, really add life to drawings. A nice instrument, but not a silver bullet.