Q: how to transfer photo from mac book to external drive so i have more storage on i cloud

Do you mean the whole Photos library

Export it from Photos, copy it to the external, and then delete it from Photos.

You don't actually need to delete any photos from your library or move them to an external drive to save space in the cloud.

If you turn off iCloud photo library on your mac (photos > preferences > cloud) and then disable and delete it in the cloud (system preferences > iCloud > manage > photo library > disable and delete) you can keep your library exactly as it is and free up the space in the cloud. If you still wish to move the library to an external drive, all you need to do is to drag the whole library to the drive. You will find the library in your pictures folder unless you have moved it yourself. Your drive will need to be Mac OS extended.

Article is for iPhoto, but the basics are the same.

iPhoto: Move your iPhoto library to a new location

Moving your library to an external drive won't save any space in iCloud unless you disable iCloud photo library which you can already do without moving it.