how to see all tables/object in db

Hello gurus PG,
Here are my  novice questions:
1- how to see all tables/objects  in a db , in psql I  tried:  list
tables  or describe table none will work . And can't find to much info
in online  PG docs
2- how to see all the  ( active or not) user connections,: users names,
hosts , apps_name. cmd running etc  in a db ?
3- how to kill  a user connection in  PG cluster db ?

thanks in advance
Isabella