How do I see what is stored on the cloud?

Either by signing in with your Apple ID on iCloud.com and you can access whatever is stored here.

(A) You can also access your stored data from the Files application just by FILES > BROWSE > iCLOUD DRIVE

(B) And finally if you want to see what is stored and using up your iCloud storage, then you can go to SETTINGS > tap on your Apple ID (your name) > then tap iCLOUD > MANAGE STORAGE

or you can just say to Siri “iCloud Settings” this is the same process as (B)

I do hope this answers your question