How can I move files from my Dropbox account to iCloud on iOS?

You cannot transfer from Dropbox to iCloud Files on iOS, but you can Copy. Open the Files app, click on Dropbox location, click select at the top-right, check the folder/files, click Move at bottom, choose Dropbox, and Copy. 

Sorry but your suggestion or instruction not clear?  Best use Microsoft snipping tool and snapshot what is to be done step by step into a Word or PDF doc as attachment would be very helpful as I reached the 2 G max and I have 15G icloud on my iPad so i really not interested to Upgrade for 1T whihc it too much  as i have Time Machine on my MacBook Pro !

Gregor, Many thank you for your attempt to explain. No notes ,makes hard interpret this statement “This is all done within the iOS Files app. ”

i don’t know how to get to this screen on the iPad ..for a start 

You need the newest versions of iOS installed to get the 'Files' app

“This is all done within the iOS Files app. You must of iOS v11 or greater. “How does one get this iOS files App? I don’t think it’s part of standard OSX 12 .x app on iPad. Where did you get your iOS Files app mate ? My OSX is very current 12.2.

It does come with standard iOS out of the box. You can reinstall it from the App Store if it has been deleted. 

Is it File Manager - Network Explorer by LDDevelSoftware ? Or something else mate ?

No, it is Files by Apple.