The metal is a solder mask so the solder only goes onto the metal pads on the board. It's thickness determines how much solder is applied. Too much, you get a short circuit. Too little and the component falls off.
Here's what it looks like after the solder is applied and after the component are placed.
After that, just put it on a hot plate or an oven dedicated to electronics, heat until 180°C and make sure all of the parts are properly aligned while the solder is still liquid.
And that's pretty much it for surface mount soldering. These boards also have through-hole components, but that's a more common skill, so I'll skip over that for now.
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