To copy content between emails, you will want to click into the original email you have created & make sure you're on the design page if you're in an email campaign.

From there, you'll want to click on the </> icon in the top righthand corner and copy all of the MJML code on the lefthand side. Always copy that specific option - never HTML. You can copy it by highlighting all of the text, right clicking & choosing "copy"

After copying that code, you can hop out of that email & into to the newer one where you want to share your content. When you're in the editor for this email, you'll want to click on the down arrow in the top right hand corner (right beside that </> icon) and paste that code you copied.

You'll finalize by hitting the import button and the previously email content should now be available in this email!