Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.
If you have an iCloud subscription, you will receive a monthly bill from Apple, check your email box.
You pay monthly for iCloud storage.
If you have upgraded iCloud storage, it would take about 1 to 3 business days in order to process.
Once your request for iCloud+ has been activated, you should receive an invoice in your email box.
See the following Apple articles:
Check your iCloud storage online or on any device
Check your iCloud storage online or on any device – Apple Support (UK)
How to use iCloud on iPhone
How to use iCloud on iPhone – Apple Support (UK)
What's in Others in your iCloud storage
What's in Others in your iCloud storage - Apple Support