What happens when I delete my photos ?

It depends on just what you mean by "delete." Usually, when you delete a picture on your iPhone, the file goes into the Recently Deleted "album." Then you have 30 days to recover it. After that it is no longer retrievable. But you can also delete a picture immediately, if you want. If you use iCloud to sync your pictures with other devices, deleting a picture from your phone will erase it from all your synced devices.

But I said "usually" and "if," so you should look at this article:

Delete photos on your iPhone or iPad - Apple Support