Reply All:
This tool allows you to reply to the sender of the original email. Enter your text in the pop-up box that appears when choose this option. When you're happy with your reply, press 'Send'.
Reply:
This tool allows you to reply to the sender and the other recipients of the original email. Enter youre reply to everyone in the pop-up box that appears when you choose this option. When you're happy with your reply, press 'Send'.
Forward:
The forwarding of emails allows you to send an email you've received on to someone else. Once you've pressed the Forward button in the Toolbar, choose the recipient and add a message in the email-field if need be.