Contacts enables you to create groups, so you can email multiple contacts just by using the name of the group.
There are a number of options for creating contacts. You can sync via iCloud to pull them in from your iPhone. You can type them manually. And you can import them from other internet accounts. Or, you can import files in a variety of formats such as .vcf. Contacts is even smart enough to monitor apps like Mail and suggest additions to a contact, such as a new email address, if it finds something it thinks is relevant.