Why am I charged $2.99 every month for I cloud storage?

You are being charged because you have subscribed to an iCloud storage plan... That's how subscriptions work. You can downgrade to the free 5GB storage plan at any time.

Open Settings>Your Name>iCloud>Manage Storage>Change Storage Plan.

So when you need more storage in your icloud, you will be charged extra for it.

If you don't want to pay the 2.99 your iCloud will not back up the entire phones information, only what the storage allows.

Also you can delete stuff if you don't want to pay it

You can delete stuff to keep your iCloud storage down. You could switch it off altogether. You can back up using iTunes on a computer or Mac

iCloud will not back up the entire phones information, only what the storage allows.

That's not accurate. Backups are all or nothing. If there isn't enough room for the entire backup, then nothing is backed up.