This functionality is disabled by default on the Cart page. You should enable it here:
Settings > Save & Share Cart > Show Button on Cart Page [tick]
A customer or administrator sending a cart from the front-end is done in the same way as above. Each field is much the same and should be filled out accordingly.
The difference is that the cart is compiled by the normal shopping experience on the front-end of the site. Products are added to the cart from the products page
When you click through to the Cart page you will be presented with the Email Cart link on the bottom left of the cart
Clicking the email cart will open the email form for the customer/ administrator to fill in the details and send the email.
The user will see a notification on a successful send.