With email marketing, you get people to opt in to your email list and then you send them emails.
It really is that simple.
The problem is, with the amount of email spam going on, you really need to set it up with them opting in to your list. I use a double opt in format, i.e they opt in and then they get sent an email that asks them to confirm that they really did opt in.
Also you need to tell them why they are opting in. A lot of email marketers us an incentive e.g a free ebook to get people to opt in to their list. Make sure that it is clear that as well as getting this ebook, they will be getting updates from you from time to time
A good article on this is
email marketing basics
I hope it helps