Hi Emma, Thanks for posting.
I think you mean how to arrange your colors on a palette, right?
If you are using transparent pigments you can use only three.
They are listed here in the forum..
  Painting on Location with Color
  Painting with Primary Colors
  Yellow, Magenta and Cyan Paintings.
  Transparent pigment triad w/ pictures

If you are useing 5, 6 or 12 pigments they are listed here along with a lot of other information you can use.
http://www.realcolorwheel.com/RCWDS.htm

5 color watercolor palette.
Nickel Dioxine Yellow PY153 (or) cool Indian Yellow PG10F
Burnt Sienna natural,  PBr7
Magenta, PR122
Ultramarine Blue, PB29
Cyan, PB15

6 color watercolor palette.
Nickel complex PY153 or PG10F
Burnt Sienna natural,  PBr7
Magenta, PR122 or PV19 (warm)
Dioxazine Purple, PV23 R/s
Ultramarine Blue, PB29
Cyan, PB15.3

12 color watercolor palette.
Nickel Dioxine Yellow Py153 or PG10F Yellow for greens.
Cad Yellow Light, PY35
Burnt Sienna natural,  PBr7
Venetian Red Oxide, PR101
Quinacridone Magenta, PR122
Carbazole Violet, PV23 R/s
Ultramarine Blue, PB29
Cobalt Blue, PB28
Pathalo Cyan, PB15
Turquoise, PB15 / PG36
Green, PG7
Yellow Green
Green Gold PG129 and PV19 Rose have got to be the next two color additions.

Making the palette itself..
If your are using acrylics the paint must be kept moist. Here is my acrylic closing box palette, it opens with the flick of the wrist.



I like a rotating palette for oils. This one you hold by a small wheel knob on the center of the bottom. It spins putting the colors you are using at the top. Here is a picture of my palette.