Q: how do i add more things to my icloud storage so that i can free up space on my iphone?

What do you want to add?

iCloud can store your numbers and pages documents.  It holds you e-mail, calendars and contacts.

Not sure what you want to do.

If you have lots of photos and you want them available at all times, one way to free up space on your iPhone is to use iCloud Photo Library:

iCloud: Use iCloud Photo Library on your iOS device

See the section on "Optimize storage on your device" in the above.

If you don't need access to those photos, you can transfer them to your computer:

Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support

and then delete them from your device.

Generally speaking, using iCloud with apps does not free up space on your device.  For example, if using iCloud for Pages, or Numbers documents, your device still caches local copies of those documents so you can work offline with them.  In that sort of use, iCloud is mainly a synchronization server, not a separate or distinct offsite storage system.  Even photo library still cache pictures on your device.

This is how iCloud is designed - it is primarily intended as online synchronization storage to allow for use of material on multiple devices you own or control.  It is not intended for use as separate offsite storage or backup.  As such, with the exception of your actual iCloud device backup file(s), almost everything that is in your iCloud space is also taking up local file cache space on your device(s) that use that iCloud account and feature.

If you need to make space on your device, you can outright delete Apps you do not use, delete documents you sync via iClouds to remove the local cached copy (which will also sync and thus delete the iCloud copy).  You can use iTunes to move photos, ebooks, pdfs, music, podcasts, and other content to your computer for safe keeping and backup and thus remove them from your device itself.

But if you need to remove content and archive it or back it up somewhere, then iCloud is really not the service for that.