Jings are a great way to share information with others. Sometimes, you want to take screen images that you can't access at school and still use them as part of a larger presentation. Sometimes, you want to share information about how to access or perform something on the computer and you need a visual. Jing is your answer.
Jing is software, it's not web based, so you have to download it. When using Jing, you have a 5 minute maximum in which to convey your screencast. You can do as many 5 minute casts as you'd like, but they max out at 5 minutes. This is first seen as a drawback, but really is a benefit since learning is much more easily tolerated in short bursts--even for colleagues and other adults.
Jing is a TechSmith product and be downloaded here:http://www.techsmith.com/jing.html
For what you'll do with it, stick to the free version!