One of the most basic but most important logic of Google Universal Analytics is to understand how these base metrics are defined. All other advanced metrics are in some way or other are dependent on these metrics and If you have to understand
how google analytics works then understanding these metrics is key to your google analytics knowledge.
Lets start with official definition of each of these metrics.
1 Session: A session is a group of interactions that take place on your website within a given time frame.
2Users: Total number of users to your property for the requested time period.
3New visitor: The number of users whose session on your property was marked as a first-time session.
4Returning visitor: The number of users whose session on your property was marked as second or more time.