Use your login and password to sign in to Gmail. Open the email you want to save.
You will see a gear-shaped icon at the top right corner of the page. You have to click it and find the Settings options that will come in the pull down menu.
Near the top of the centre you will find a Labs tab. Click it.
Scroll down a bit to find Enable. Click it and go to ‘Create a Document’ option. It will be the last option in the pull down menu.
Save Changes is the option that is placed at the bottom as well as at the top of the page so you can go anywhere to choose that. This step should be followed after Creating a Document.
You will have to do all the above stated steps when saving the email for the first time. Otherwise you just have to go to the ‘More’ option at the found at the Menu bar above the email and click Create a Document.