The answer is likely going to be dependent on which email program you are using.
Assuming the built in "Mail" app, native to Windows 10 .....
From the Menu bar, on the "New mail" window, select the "insert" tab and select "Files" with the adjacent paperclip
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.