halo 3 claiming a skull?

[Joahua S]

i dont know how to claim a skull on halo3 im on legendary and im not sure what to do.... i know were it is but it wont give me a achievement please help

 

[knightofyourmom]

Few things:

Doesn't have to be on legendary
Must be ABOVE easy.
Only golden skulls will give the achievment

You MUST start from the BEGINNING of the level.