someone walk me through buying more storage on iphone?

Before paying, look at Settings > General > iPhone Storage. It shows what's actually eating the space, and there's an offload unused apps option that removes apps you never open but keeps their data. Often clears more than you'd think.

worth separating the two things — you can't add storage to the phone itself, that's fixed at whatever you bought. what's actually on sale is icloud space. settings, your name at the top, icloud, and the upgrade option is in there. buying it doesn't free up the phone by itself though. it only helps on-device once you turn on optimise photos, which keeps small copies locally and the full ones in the cloud.