There're plenty of books, e.g. http://www.ccs.neu.edu/home/matthias/BTML/ is very good. As a working professional with 15 years experience who has only gotten into strong inferred typing relatively recently I consider it a godsend; I wish I'd known about it from day 1.

Most of the popular languages have a beginners mailing list, so just join that, ask questions if you're stuck, answer questions as you learn more. To "get involved" in open source, solve one of your own problems, tidy up the code, upload it to GitHub or wherever and announce it on the list.