Is there a training program for iCloud and how to use it effectively. I have downloaded the booklet but not sure how I access files, photos saved on iCloud.

I am trying to understand cloud but have very little information for a non technical person. Is there any product that I can access that will provide me with step by step details on how to access things stored in Icloud. I have recenly lost all my data on my external hard drive and thought that I could restore through icloud.