Open Gmail and sign in
Click Compose
Enter the recipient, subject, and message
Open the email you want to attach in a separate window or tab
Click and drag the email into the compose window, if supported
Or click the three-dot menu on the email
Select Forward
Send the forwarded email
Or download the email as an .eml file from your email client
In Gmail compose, click the paperclip icon
Select the saved .eml file
Click Open
Send the email