User Information

id prints information about the given user
     id picklu //print information about user(including uid, gid, groups, etc)

whoami  //prints the user name associated with the current effective user ID.

groups //prints the names of the primary and any supplementary groups for each

fingers  //displays information about the system users

who      //show who is logged on
      who -a      show all users log on to the system in different terminal.

su allows one user to temporarily become another user
     su          become root user
     su -        become root user with all the all the environment
     su -  change to supplied user