General questions on iPhotos

I have the latest iPhone but an older Macbook Air (2015). I'm in the process of migrating photos from Google Photos back into iPhoto. I have iCloud enabled, but am running into storage issues on the older Macbook. Where are the actually photos I take stored? iPhone? iPhoto on Mac? or iCloud?

I have thousands and thousands of photos. My iPhone storage shows about 6GB of photos, but my Macbook shows 22GB. Where are they actually stored?