Got email stating that I'm out of iCloud storage, how can I check?

I got an email from my gmail account stating that I am out of icloud storage and I can now not receive email to this account, and I am not sure how to see my storage levels because in one section in the settings I saw that I have only used 3gb of the 15gb allowed. Please advice.

Many thanks,

Nola L.

[Edited by Moderator]