Actually Urdu is not the only language in Pakistan, you also heard people who speaks Balti, Kohistani & Shina (in Northern Area).
You can take a look of this website at http://www.softjamboree.com/article/write-urdu.html on how to write Urdu. However, if you want to have a first glance on Urdu, I'd recommend you to take a look of Lonely Planet Phrase Book, it is not a perfect book, but I really let you know to what extent you really like this language.