Email marketing is basically sending direct promotional emails in an effort to send new customers or existing ones to your website, for it to convert 'the sale' of your product or service.
The killer with email marketing is that once the emails have been set up, they are then sent at pre scheduled times to your email list. This makes it 100% automated. You don't need to put any extra time or effort into it.
The idea is that you gradually build up a relationship with your potental customers, keeping you in the front of their minds when a sale is required.
The email may be an announcement of a special offer. Generally, a mailing list is used, of which can be purchased or can be collated in a number of ways.
Skilled email marketers attract an audience of people who want to get their emails, usually by offering free information or promotional material pertaining to their interest and then they send them offers for products or services based on these interests.
The list can be targeted to any directly specific groups, for instance people interested in 'Egyptian cotton luxury towels'.
Email marketing software allows you to monitor the campaign, such as seeing who opened the emails, and when, and even who they forwarded them to.
This gives vital information that can be used to find out % conversions and ways to 'tweak' the email campaign.