What happened to the origional cast of "That 70's Show?"?

I watch the reruns on The CW and had no idea there where any newer ones. I watched one from season 9 i think. Some guy was there who I think was Kelso. And Eric was completely gone. Please tell me when and what happened to each character! Also is that the same Fezz? Can you summerize what happened after High School to me? Thanks!