Can anyone explain to me the difference between the cloud storage sites - Microsoft, Icloud, Google etc.  

Microsoft keeps popping up on my computer wanting to set up cloud storage

Apple Icloud storage charges me $0.99 a month to expand my storage (I use my photos for that)

Then Google storage charges me a per year fee and if I don’t pay keeps telling I might not get my emails if my “storage” fills up.

I would appreciate if someone could explain this all to me.  I don’t think I need 3 different cloud storage.

Thanks