Reinstalling OSX without media

I don't need to yet as only just bought the machine. But unlike my previous macpro my new imac has no CD drive or media.

I read through the community and cannot find the info. Can anyone point me to the directions to clean install. I want to know before I hit an issue.

On a sepearte issue, I was thinking of formatting my old laptop, do I need to download lion then mountain lion or can I skip lion? I have the original discs for this machine... or can I follow a quicker route?

Steve L