how do i find iPhoto on my iMac?

How do I seriously get this installed and set up?? I have tried for a week, and yes I look it all up. And...yes - I am a new apple looser...and feel like I have been introduced to a new world, and cant manage to do anything.

I cannot find iphoto on my imac.

I cannot "choos" Photo stream icon in my icloud..which I am also trying to get set-up.

Please help!!