Summarize:

Click the "Mail" link next to the picture of an envelope in the top right corner of the main Yahoo.com page. Click the "Compose" button on the left side of the screen to start a new email. Click the "Inbox" button on the left side of the screen to browse a list of the emails you have been sent. Note that, by default, your Yahoo email account displays your inbox as soon as you log in. Click on an email you've been sent in your inbox. Pick a reply option with the buttons at the top left of the email. You can reply normally (curving arrow pointing left), reply to all (multiple curving arrows; used when you are one of multiple recipients), or forward the message (straight arrow pointing right). In your email inbox, click the icon that looks like an address book in the top left. This will bring you to a list of your online contacts. To add a new contact to the list (which will be blank if you've just created an account), click "New Contact" in the top left. You can also choose to import contacts from a social media profile by clicking one of the buttons in the center of the screen and following the prompts. Having someone in your list of contacts gives you several benefits. For instance, you don't have to remember this person's email address — you can just start typing his or her name in the "To:" field of your email and it will display automatically. This is especially useful when you need to send a single email to many recipients.
Access your email account. Send new emails: View emails you've received. Reply to emails. View your contacts.