Summarize:

If you live in Pennsylvania, there are several places that offer Pennsylvania Dutch classes, including Pennsilfaanish Deitsch Friend Groups (the Amish equivalent of churches), some universities, and some public libraries. The Pennsylvania German Society maintains a list of places that offer lessons and classes. There are not many printed sources in Pennsylvania Dutch, because it is primarily a spoken dialect, but there are some that will help you become a fluent reader. The Pennsylvania Dutch Dialect Project includes a variety of short texts in the language, including jokes! The German-Pennsylvanian Association maintains a website and blog that is mostly written in the language. The Pennsylvania German Society publishes a journal, Der Reggeboge, that includes dialect pieces and columns. The "Pennsylvania Dutch Blog" sometimes features pieces written in the dialect. Pennsylvania native Brad Humble maintains a blog, "Brad Humble's Amish Country," on Amish culture and language that includes a cookbook, dictionary, and list of phrases. Because Pennsylvania Dutch is often pronounced quite differently from modern German, it's important to listen to native speakers and attend to their pronunciation. The University of Wisconsin at Madison has collected a bunch of audio interviews with Amish speakers, with transcripts provided. Hiwwe wie Driwwe has its own YouTube channel with videos in spoken Pennsylvania Dutch. If you're really serious about learning more about Amish culture and language, there are some colleges and universities that can help you. Millersville University, Kutztown University, and Elizabethtown College (all located in Pennsylvania) all have centers for the study of Pennsylvania German culture and language.
Check if there are classes available in your area. Read as much as you can in the language. Listen to spoken Pennsylvania Dutch. Attend a college that has resources for Amish study.