A number of good presentation exist that explain or cover OAuth. Many can be found on Slideshare.

Here are few examples: 

• Advanced OAuth Wrangling (EN) by Kellan Elliott-McCrea
• Web 2.0: The how of OAuth (EN) by Scott Fleckenstein
• Introduction to OAuth (EN) by Eran Hammer
• OAuth FTW (EN) by Chris Messina
• Integrating services with OAuth (EN) by Luca Mearelli