DO doesn't provide any application installer that will setup a fully working mail server for you. The 'one-click wordpress' application only creates a Wordpress website on your droplet, with ofcourse the needed software on your droplet to host it.
If you would like to use your droplet as a mail server, you need to manually setup all the software and configure it. However I believe I saw a topic lately about DO blocking mail ports against spam servers.
Since you don't have any experience and also didn't know that for example Wordpress application doesn't setup a mailserver for you, I suggest you pay for your own mail accounts at some third party company. You could for example check at Namecheap, Rackspace or any other company