Need help with Backing up Sessions

Hello,

Today as I was trying to save space, I deleted recent files on my IMAC only to find that when trying to open C1, couldn't find the session :(  After research I found that I can click on the file and select put back- but after doing this, I tried to select on my external, only to find that I'm out of space and it wouldn't not open, unless I dragged it off my external to my desktop. URG

I just downloaded sync folder pro, and must have not set that up correctly because it filled my external up.

So if anyone can give me a guide step by step approach on how 

1. Back up the Session

2.Back up as I'm shooting( I mainly shoot headshots)

3 How to utilize  iCloud, I do have a box account.

any help would be appreciated. 

Thanks.

Steven