GlideSession is often confused, for me at least, with gs. You need to
make a gs call to get the session, but the session itself has very
specific functions that can be really useful. Below I go over those.
Here's a link to the
docs.

<!--

GlideSession

--

clearClientData

Clears a session client value previously set with putClientData().

This method is used in a client script to clear data values that were
set by a server script using the putClientData() method.

var session = gs.getSession();
session.putClientData('custName', 'Harry');
var clientData = session.getClientData('custName');
gs.info(clientData);

session.clearClientData('custName');
clientData = session.getClientData('custName');
gs.info(clientData);
/**
 * Harry
 *
 * null
 */

getClientData

Gets a session client value previously set with putClientData().

This method is used in a client script to retrieve data values that were
set by a server script that used the putClientData() method.

var session = gs.getSession();
session.putClientData('test1', 'Harry');
var clientData = session.getClientData('test1');
gs.info(clientData);
/*
 * Harry
 */

getClientIP

Returns the client IP address.

var session = gs.getSession();
var addr = session.getClientIP();
gs.info(addr);
// 50.59.164.97

getCurrentApplicationId

Returns the application currently selected in the application picker.

This method requires admin privileges.

var session = gs.getSession();
var appID = session.getCurrentApplicationId();
gs.info(appID);
// ce05b9f32b840200c5244f74b4da1501

getLanguage

Gets the session's language code.

var session = gs.getSession();
var language = session.getLanguage();
gs.info(language);
/**
 * en
 */

getSessionToken

Returns the session token.

var session = gs.getSession();
var token = session.getSessionToken();
gs.info(token);
// 4284b5372b840200c5244f74b4da15f2c3476cf7fcb6572afa4ef9d5e6d307a5fd9e1da7

getRoles

Gets a list of roles for the current user.

The list of roles does not reflect any changes made during the current
user session. To get the updated list of roles, the user must log out
and log back in.

gs.info(gs.getSession().getRoles());
// admin,hr_fulfiller,itsa_fulfiller,security_admin

getTimeZoneName

Gets the name of the session's time zone.

var session = gs.getSession();
var zoneName = session.getTimeZoneName();
gs.info(zoneName);
// US/Pacific

getUrlOnStack

Returns the URL on the stack. Returns null if the stack is empty.

var session = gs.getSession();
var URL = session.getUrlOnStack();
gs.info(URL);
// sys_app.do?sys_id=ce05b9f32b840200c5244f74b4da1501&sysparm_goto_url=sys_app.do%3Fsys_id%3Dce05b9f32b840200c5244f74b4da1501

isImpersonating

Returns true if the user is impersonating another user.

var isImpersonator = gs.getSession().isImpersonating();
gs.info(isImpersonator);
// true

isInteractive

Determines if the current session is interactive.

An interactive session is one that involves an end-user interacting with
a user interface that then retrieves information from a server. An
example of this type of session is when a user logs in using the log-in
screen or uses a form to query a data store. A non-interactive session
is one that only involves programmatic interaction with a server such as
a SOAP request to retrieve data.

var interActive = gs.getSession().isInteractive();
gs.info(interActive);
// false

isLoggedIn

Determines if the current user is currently logged in.

var session = gs.getSession();
var loggedIn = session.isLoggedIn();
gs.info(loggedIn);
// true

putClientData

Sets a session client value that can be retrieved with getClientData().
This method is used in a server side script that runs when a form is
created.

var session = gs.getSession();
session.putClientData('test1', 'Harry');
var clientData = session.getClientData('test1');
gs.info(clientData);
// Harry