Is there any way to buy more storage for my iPad

In addition to Bob Timmons' answer.

There is a difference between your iPad's internal memory and iCloud. As mentioned, iCloud is only for backup - it will not expand the memory on your iPad.

You can see what is taking up space on your iPad here:

Settings → General → iPad Storage

You can read about the difference between iCloud and the internal memory here:

What's the difference between device storage and iCloud storage? - Apple Support

Mila1313 Said:

"Is there any way to buy more storage for my iPad"

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Try Clearing "Other" Storage:

"Other" is all "junk" (as we'd commonly say) from installed apps (i.e. caches). So, to fix this, first backup* your iPad and then restore** it from the backup. See where things go from there.

* Backing Up: How to back up your iPhone, iPad, and iPod touch - Apple Support

** Restoring: Restore your iPhone, iPad, or iPod touch from a backup - Apple Suopport

Storage is fixed on the iPad (and iPhone), but you can purchase storage on iCloud for backups, etc.

Upgrade to iCloud+ - Apple Support