Hi,
i'm having troubles crating siganges like the square(texture signage/shape03.
When i create a brush with that texture, then its just white and transparent.
How do i create them?

You'll want to place them as overlays, with only a few exceptions.

Ginso wrote:
When i create a brush with that texture, then its just white and transparent.
How do i create them?

Hi. That's probably because it's created to be used as an overlay, as Felix said, so if you use it as a common brush texture, you are watching its alpha channel. The content of that material is:

UnlitGeneric
{
$basetexture "signage/shape05"
$surfaceprop default
$selfillum 1
$decal 1
"%keywords" portal2
}

So to avoid that issue, you'll need to remove the lines $decal 1 and $selfillum 1, and it's recommendable to use the shader "LightmappedGeneric" instead of the "UnlitGeneric"