If you have a apple devices ie : iphone ipad / mac in any combination then iCloud is the thing that binds them all together (I will talk about windows in another post).
When you buy / use an apple device its compulsory to have an apple ID / AKA an icloud account. The exception to this is using a Mac (You can decline to turn it on but not wise)
When you take photos on your Iphone or ipad , the initial photo is on the device which is limited by the devices storage, to this end unless you have turned it off, then the photos then upload to your icloud account.
The photo Uploads to icloud at its maximum resolution and the photo on the device then keeps a lesser quality photo on the phone or ipad to conserve storage on the device.
The icloud account size is limited till you pay for extra storage - if you don't then eventually it will become full and no more photos will be stored, so really you need to increment your storage to the next level.
The key thing is that all the devices need to be using the same apple ID (Icloud Account) and you need to have sufficient storage for the photos in icloud - To Give you a rough idea 50GB of storage is 79 pence a month - I have 9500 Photos and videos these take up 56GB of storage so i subscribe to the next level up @ £2.49 for 200GB. This is tons of space.
Last thing is when you switch all your accounts on then be patient and let all the photos upload, stay connected on wifi, and if you want to speed the whole process up, then keep your device switched on maybe overnight and switch off auto lock and leave it plugged in , so it stay's connected and keeps uploading. Once its done then it will add photos automatically 🙂
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