To transfer the photos select them in photos and export (file menu ==> export) to a desktop folder and drag the folder to a mounted, unlocked flash drive large enough to hold them and take them to the other computer
On the other hand if you want to transfer the Photos library which contains much more than just the photos you need to be sure the flash drive is formatted Mac OS extended (journaled) and quit Photos and drag the Photos library to a properl;u formatted flash drive large enough to hold it and take it to the other system and drag it to the pictures folder there (be careful not to overwrite an existing Photos library - if there is one you need to change the name of one of them) and double click on it there to open it
LN