Here are some videos that outline the four basic serves that beginners can focus on to start:

https://www.youtube.com/watch?v=EnxI1XTKC9k

The bounce serve has been finally approved in the rulebook. It has some advantages from the basic serve especially if you are having trouble getting your serves on target:

https://ca.video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=Youtube+Picklball+bounce+serve&type=E211CA1494G0#id=6&vid=826e385a168078051ec748e047e25b06&action=click

Here is another video that breaks the drop serve into various attack modes:

https://ca.video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=Youtube+Picklball+bounce+serve&type=E211CA1494G0#id=3&vid=e2dd4afaf5e049da2702dfeda0a644a6&action=view