Doubts with WordPress Multisite User Management

I have a project and will be using Multisite feature of WordPress. I have few questions regarding this:

• if i add a user for the main site, will it share the user for all sites?

• if that user I created is logged in to the main site, will the session be shared for the sub site?

For example:

1. I log in to the main site domain.com

2. Then I move to the other site site1.domain.com

Is the session being shared from the main site and the sub site?

Yes, the users in one site of the network are recognized as such, and have subscriber capabilities (read and post comments) in all the network.

If they are logged in one site of the network, they will see the Admin bar when visiting the other sites.

If they try to access the dashboard of other sites they receive this notice:

Check this other answer I just gave here in SO: Wordpress WPMU Login consistency across multisite network