How can I unsubscribe, opt out and get rid of iCloud, iMessage etc.?

Save any photo stream photos that you want to keep to your camera roll, email any synced notes that you want to keep to yourself, then go to Settings>iCloud, tap Delete Account, provide your password and choose Keep on My iDevice when prompted.

To stop using iMessage (which isn't part of iCloud), go to Settings>Messages>Send & Receive, tap the ID and sign out.

I have an old Mac desktop--2007--and it's running Mavericks. I have an ipod touch that's about 5 years old and a new Mac Book Air so I thought it would be good to sync them. I started with Calendar and immediately started losing appointments. Decided I'd rather sync the old fashioned way but when I try to uncheck Calendar a popup says "Calendars stored in icloud will be deleted from this Mac." I cannot to afford to lose everything from my desktop Calendar; it's got--or had--everything going back to 2007. Is it even possible, without being a computer geek, to opt out of icloud?

Aas your calendars are actually stored on the iCloud server they will not be accessible once you sign out. You will need to move them back to being on your Mac. Please follow the second set of numbered instructions here:

http://www.wilmut.webspace.virginmedia.com/notes/icloudmovecalendars.html