The joke is that the Pope's tweet is full of street or ghetto slang like 'homie' (=friend), and Da (=the). His actual tweet said, "Dear friends, I am pleased to get in touch with you through Twitter. Thank you for your generous response. I bless all of you from my heart."
You say Your Holiness when you address the Pope or the leaders of some other religions.
If you get the hang of something such as as skill or activity, you begin to understand or realize how to do it. • It's bit tricky at first till you get the hang of it.