There are various plugins to collect user data and MailChimp is a company that allows you to send up to 2000 emails for free a month. MailChimp supplies templates and you can, with some integration create newsletters from your blog posts. On your WordPress website, you can have a pop up box to subscribe to your newsletter or you can have a static form. There are different mailing systems available but you must get people to subscribe or you will be blacklisted for spamming if too many people unsubscribe. There are different systems available to collect data, MailChimp is free for the first 2000 emails but then there is a price plan depending on your usage per month.