Most landing pages you will see seek to obtain an email address to subscribe the website visitor to your newsletter (also known as an AutoResponder).

A newsletter or autoresponder is simply a series of emails that go out at a pre-scheduled time in the future. It's all automated. You may have heard of MailChimp, GetResponse or AWeber. Each of these are prime candidates to help you setup a newsletter or autoresponder. Basically, because they go out automatically, you can "say" that your are marketing while you sleep! :-)

Regardless, it's fairly easy to do with one of the available plugins from the WordPress Plugin repository:

https://wordpress.org/plugins/

This is a free landing page or "Squeeze" page that came with my GetResponse account where I have my newsletter setup.....