My iPhone storage is almost full so I brought a storage but I can’t use it please help
iPhone 6s, iOS 15
iPhone storage cannot be increased in size. The only way to increase the iPhone storage is to purchase a newer phone with more storage space.
See this discussion on the difference between the phone storage and iCloud storage.
What's the difference between device storage and iCloud storage? - Apple Support
If you are using iCloud Photos, you can enable "Optimize iPhone Storage."
When you are using iCloud Photos, full-size copies of your photos and videos live on Apple's servers in iCloud. They normally also live in device storage on each device (iPhone, iPad, Mac) connected to iCloud Photos. But enabling "Optimize iPhone Storage" gives the iPhone to substitute "space-saving" (lower-quality) copies in its device storage, as needed, to free up some device storage. (The idea is that you can download full-size copies again, later, on an as-needed basis, when you're connected to the Internet.)
I brought a space on iCloud but I can’t use it
