Your pitches and press releases will be sent from your account email address by default. And when a recipient replies from their email account, you would receive the reply in the From email address directly.
If you are on Standard, Professional or other supported plan, you can add other email addresses as the From address. To do this, click in the From field in the pitch composing window. The email address added would receive a verification email for verification and confirmation purpose. Once the email is verified it can be used as a From address.