Every time I turn my iPhone or iPad on I get the message 'your icloud storage is almost full' or 'you've used 4.7G of your 5G allowance on iCloud'

But to the best of my knowledge I haven't been knowingly storing anything on iCloud. I'm assuming it (iPhone / iPad) is doing it automatically or something?

My question is - how can you actually see what's stored in your iCloud account?

I logged into iCloud last night,but I couldn't actually see what was stored in it or how to delete anything that is stored in it

I'm sick of getting these messages every time I turn on the iPad / iPhone and don't want to pay $$ to increase my iCloud storage - I'd rather  see what's in there and delete anything I don't need....

any advice would be appreciated