The first map for my world

[Revuscuan]

Thanks, but what do I have to do to open the pallete?

[Revock]

Thanks, but what do I have to do to open the pallete?

Look for the Palettes tab, double click on a palette to open it and click on the desired color, if you don't have that tab add it to the toolbox:

adding a tab step one (although you can see palettes is already added)

here i would select whichever tab i wanted to add.
These screenies are from my linux box, there adding palettes, bruches etc. to their respective folders is done in: /usr/share/gimp/2.0/
in Win8 (64bit gimp) its: C:\Users\username\gimp-2.8\
in WinXP its C:\Documents and Settings\username\.gimp-2.8\