Nazi Zaku Zulu!

What did you paint this with?

...Did you thin your paints?

you really need to thin out your paints. dont slap paint on the kit on a whim...
for a second i thought it was a bootleg toy

exactly.. the result made it look like a bootleg. Im a novice at painting, so i practiced on this lol. i mix around 4 part thinner to 6 part paint.. is that enough?

and how to layer?

Maybe you used too much paint, did you use acrylic paints ? I guess the enamel paints are better to use with a brush because they don't leave too many brush marks. To use layers you just need to thin the paint more than when you don't use layers. When you thin your paint, you can use different ratios of mixing, like: brushi 1/2 (thinner | paint) and for airbrush 2/1 or more thinner ,if you want to use more layers (like 3/1, 4/1). Sorry for my bad english and wait to see what the people here say, they usually help a lot xD

Some tips:
1.) THINK about what kind of paint job you want on a kit BEFORE building it. That way, you can actually paint parts of your kit BEFORE putting it together, it will be easier for you.
2.) I STRONGLY suggest you either use a spray-on Primer or a topcoat spray on your kits prior to painting. Not a thick coat, just enough to cover the kit entirely. This gives your kit a thin surface to paint over.
3.) Use different types of brushes for what you need. Don't use one brush for EVERYTHING. I'm lazy and use 3-4 brushes on one model, others might use more.
4.) I've personally made this mistake countless times: USE PROPER MASKING TAPE if you have to paint two-three different colors on the same surface.

You live in Singapore, so humidity may be a factor--some of my early (and crappy) Gunpla work was when I lived in the Philippines. I'm fairly sure that in 6-12 months time your Nazi Zulu's paint job will chip and fall off on it's own due to the weather.

That is some thick coat of paint, lol. But for some reason it worked for the shield; gave it quite an industrial look >_<