Many people today are creating an email list for various purposes. One important reason: "The money is in the list" Well more so, the relationship you have with your list. Have you ever heard of "making money while you sleep"? or "making money on-demand". When you have an email list you can automate your business with an autoresponder and create follow up messages that way your audience can hear from you anytime.
In order to create a list you must create a "landing page" or "squeeze-page", all you have to do is find a way to get visitors to your landing page so think of providing them as someone you can help continue the journey with. In order to obtain visitors, there is both free (blogging, guest blogging, youtube) and paid traffic methods (PPC, banners, solo ads), this all depends on your budget if you go the paid route. If you go the "free" traffic route it just takes time to produce content and build an audience organically.
Setting up a mailing list properly is important and, haven't you ever heard the term "the money is in the list"? Well, it is true if you build a list of prospects and later follow up with them with more valuable information, your prospects will know, like, and trust you, and this buys recommendations from you anytime. All this is done with the power of the internet.
If you are looking to build an email list for a particular purpose, always remember to lead with value and know what your audience is looking for. Only recommend products you would personally use yourself. When building a list it is important you always respect the emails on your list as people because at the end of the day they are just real people looking for solutions and you are that person providing them that solution.