If you’re new to iPhone or iPad and have just gotten started with iOS 5, you might be wondering how to set up the new Twitter integration feature. It gives you the ability to tweet directly from Photos, YouTube, Safari, Maps, and any other third party applications that request access to your twitter settings. It’s also easy to set up. Here’s how.
  1. Go to Settings
2. Enter the Twitter Settings
3. Enter your @username and password
4. Select which apps you wish to have access to the twitter settings.
5. Now, you’ll be able to share from Photos, YouTube, Safari, Maps and other third party apps that support the twitter integration.

Bonus: When you’re in Twitter settings, you can install the official twitter app, directly from settings.
Optional: You can merge your twitter friends with your contacts. Twitter uses phone numbers and email addresses to match twitter names with your friends, and adds a link to their profile to their contact.
You’ve now got Twitter set up on your iPhone, allowing you to tweet straight from some of Apple’s native apps, as well as some third party apps. You can also login to select Twitter apps, without having to re-enter your login.