Browse All Your Files in One Place
There is a Files app that you can turn on for the iPhone 8 that connects into all of your cloud accounts allowing you to use what is basically a Finder or Explorer window to see all of your files. This includes iCloud, DropBox and other services and you can easily navigate, share, open in apps and use the files you have in the cloud.
Setup iCloud and then turn on iCloud Drive in Settings -> iCloud -> iCloud Drive. From here you will want to download any other apps you want to connect like DropBox or Box and sign into those apps and set them up.
Next, open the Files app, tap on Locations and then on Edit and turn the other services on to start using them.
Once setup, you can use these services to always see your files and then use them even without a computer.