I'm a new user, What are the best training document to go through ?

Hi Bernard, Welcome to Gainsight Community!

You have all the product documentation here, including the training videos.

These couple of overview videos and introductions may help orient you to getting started.  Most of our training and docs are geared toward roles of Admin (GS Admin/CS Ops), CSM or Manager.
https://support.gainsight.com/Getting_Started/Roles

The other resource we have our Customer Success University with a number of eLearning courses.
https://customersuccessuniversity.gainsight.com/catalog#courses

When searching for specific documentation, I recommend using the new built in help center for faster results.

What Kate said. That feature is so nice for "in the moment" help. I am a relatively seasoned user and have already enjoyed this option!

Also in the Help Center, you can find documentation relevant for that particular Gainsight app page. For example, if you are on the CoPilot page, documentation related to CoPilot will be shown in the Help Center as suggested articles, and if you are in the Report Builder, you can see documentation relevant to creating reports, and so on.