I am not sure if skulls are on the screen means that you have beat the campaign. It usually just means that you have beat the mission.
No, the skulls are found in the campaign levels on the normal difficulty or higher
on the campaign menu press X
Go to the campaign menu and press X and your skulls collection will pop up.
You have to complete achievements and levels. For example, beating the campaign on normal gets you EVA along the way. Grabbing skulls also gets you Hayubusa (aka ninja) armor (which I have).
find all 13 campaign skulls
You have to go to campaign and press x.
You have to find all the skulls in campaign mode.
press the X button on the campaign selection menu.
You can use that during campaign scoring mode along with other skulls to rack up points more easily... if they are not silver skulls. silver skulls are used to just have fun during campaign mode.
On campaign on halo 3 (difficulty normal or above) by the river on the first level jutting out on a rock theres a skull.
There are no skulls in Halo Reach.
When in the campaign lobby, press X to bring up the settings menu.