List building is all about connecting with your target audience by offering them high quality information in exchange for their subscription. Once a subscriber is a confirmed member of your list, you can begin sending promotional based follow up emails in balance with relevant and useful content based on your overall market. Email marketers (like you!) collect leads using a combination of squeeze pages and opt-in forms. These forms are generated by your autoresponder provider and are embedded into the HTML code of your squeeze page template.
Each time a visitor to your squeeze page enters in their name and email address, they are added to your mailing list database, and become an active subscriber of your newsletter. List building helps faciliate the process of converting subscribers into active customers, since once your prospect has been added to our mailing list, you are able to develop a relationship with them, that will encourage sales as well as repeat sales (which will make up the larger majority of your email marketing income).