Two Ways to Add Contacts within Webmail
1. Click the Email Address / Name
When you receive an email from someone and you want to add them to your contacts, you can click their email address and a little menu will pop up that says "add to address book". If you click that, it will automatically add their name and email to your contacts.
2. Add them manually in Contacts.
You can do this by clicking on "Contacts" and then click the "Create" button. Fill in all the information you want to keep about that person there and then click "Save" at the bottom.