How to copy iMessages from Mac to USB (iMessages location)

Find the saved messages here, along with photo attachments;

Macintosh HD/Users/(Username)/Library/Messages

If library is not found @ /(username), you are able to find it through storage management, then to messages, and select find in finder. after the finder window comes up, in the top bar select "Go" to enclosing window, and go back to find the Messages folder.