A Sender includes a name, email address, reply to email address, and bounce email address. The Sender name and email address is what appears in the From field of your emails. The reply to email address is where any replies to your emails will be sent.
Before you can send any emails, you need to have at least one verified Sender in your account. When you sign up for PushSend a Sender is automatically created with your name and email address. You can then add as many senders as you need.