I found William Irving's A Guide to the Good Life: The Ancient Art of Stoic Joy a very legible contemporary (if somewhat idiosyncratic) introduction to Stoic thought, and maybe more accessible/applicable than the classic sources.
http://classics.mit.edu/Epictetus/epicench.html
Which is quite short.
https://standardebooks.org/ebooks/epictetus/the-enchiridion/...
He gave some really great examples of how to apply stoicism in today's world.