[Topgun]

do you make the sky box with stars then add the planets and nebula in fred or do you put everything on the sky box at once? if the later, how do you add planets and stuff without it getting distorted?

[Retsof]

A skybox is usually used for a high-rez planet.  The stars are already in the "stars.pof" skybox.  You add nebulas and suns in FRED.

[Jake2447]

IIRC the star skybox is starfield.pof
another use of skyboxes is hi res planets, as retsof mentioned
an example of this is the earh skybox used in blue planet (named earthbox.pof)