yeyebaby Said:
"If I purchase iCloud, will all of my stuff on all of my devices, all photos for example, suddenly appear/synchronize in all of my current devices (iPad, iPhone, MacBook)?"
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Uploading Items to iCloud:
If you want these to be uploaded, then note two things:
Enable these items (i.e. Photos) in iCloud settings or preferences, and then they should sync. Go Here: Change your iCloud settings - Apple Support
- How Much Space is Required:
As for all of your stuff being uploaded, then that would depend on how much space you have to use. You are granted only 5GB of free iCould storage space (in particular countries). Go here to see your options: iCloud+ plans and pricing - Apple Support