I am trying to show Utube video's on my church iMac through our projector and cannot figure out an easy way to get the video from my iMac screen to the projection screen?

The first thing we need to know is exactly which model iMac you have and which model projector you have. This will help us point you to the correct video adapter/cable. Video output standards have changed dramatically over the years utilizing both analog and digital signals. Once we know which outputs and inputs each device has we can make a recommendation.

Here's an article that shows the various Apple video ports.

http://support.apple.com/kb/PH10567

Your project will likely have one or all of the following VGA (analog), DVI (digital), or HDMI ports that can be used to connect your iMac.

This article lists the various video cables and adapters available from Apple.

http://support.apple.com/kb/HT3235

I forgot to mention another option that I use at home for playing YouTube videos and other videos and photos from my iMac... The Apple TV is a wonderful and inexpensive solution as long as your projector has an HDMI input.

http://www.apple.com/appletv/

iPhones, iPads, and the more recent Mac's, support the Airplay feature which allows you to wireless display content on a projector or TV using the AppleTV. It's really awesome.