Open Source community has always helped in making the technology available to everybody. This is the community which is actually working with the moto - "That technology has to reach everybody beyond social and economic barries".
GNS3 is one such tool which helps you prepare for almost all networking related certifications, practising the lab scenarios and saves you some thousand dollars on the lab infrastructure.
Since, we believe sharing is caring, I am sharing the links to some tutorial video and guide for GNS3.
Want to have a good start with GNS3? Please watch this absolutely excellent video: GNS3 overview and operation by Jeremy Cioara from CBT Nuggets (37 minutes).
If you had developed some videos or know about videos not available in this, Please submit the link here and let more and more people get benefitted from it.