About ASP.net Session
Sessions are identified by a unique identifier that can be read by using the SessionID property.
When session state is enabled for an ASP.NET application, each request for a page in the application is examined for a SessionID value sent from the browser.
If no SessionID value is supplied, ASP.NET starts a new session and the SessionID value for that session is sent to the browser with the response.
By default, SessionID values are stored in a cookie. However, you can also configure the application to store SessionID values in the URL for a "cookieless" session.
A session is considered active as long as requests continue to be made with the same SessionID value. If the time between requests for a particular session exceeds the specified time-out value in minutes, the session is considered expired.
Requests made with an expired SessionID value result in a new session.
For more info:
ASP.NET Session State
Your Q : Can multiple users connect to the same Session created by one user?
Answer : Can't