I am reading the book Unix Power Tools, and came across the ps command. The output of command `ps x`as given in the book is :

 PID TTY STAT TIME COMMAND
 18034 tty2 S 0:00 -zsh
 18059 ? S 0:01 ssh-agent
 18088 tty2 S 0:00 sh /usr/X11R6/bin/startx
 18096 tty2 S 0:00 xinit /etc/X11/xinit/xinitrc -- :0 -auth /home/jpeek/
 18101 tty2 S 0:00 /usr/bin/gnome-session
 18123 tty2 S 0:33 enlightenment -clientId default2
 18127 tty2 S 0:01 magicdev --sm-client-id=default12
 18141 tty2 S 0:03 panel --sm-client-id default8
 18145 tty2 S 0:01 gmc --sm-client-id default10
 18166 ? S 1:20 gnomepager_applet --activate-goad-server gnomepager_a
 18172 tty2 S 0:01 gnome-terminal
 18174 tty2 S 0:00 gnome-pty-helper
 18175 pts/0 S 0:00 zsh
 18202 tty2 S 0:49 gnome-terminal
 18203 tty2 S 0:00 gnome-pty-helper
 18204 pts/1 S 0:01 zsh
 18427 pts/1 T 0:00 man zshjp
 18428 pts/1 T 0:00 sh -c /bin/gunzip -c /home/jpeek/.man/cat1/zshjp.1.gz
 18430 pts/1 T 0:03 /usr/bin/less -is
 18914 pts/1 T 0:02 vi upt3_changes.html
 1263 pts/1 T 0:00 vi urls.html
 1511 pts/1 T 0:00 less coding
 3363 pts/1 S 0:00 vi 1007.sgm
 4844 tty2 S 0:24 /usr/lib/netscape/netscape-communicator -irix-session
 4860 tty2 S 0:00 (dns helper)
 5055 pts/1 R 0:00 ps x

Can someone help in decoding this output?
What is meant by pts/0 and pts/1? 

 1. All I could find was that pts stands for "pseudo terminal slave", but couldn't understand the difference behind pts/0 and pts/1. 
 2. Why is there a "?" in TTY column? Why is the tty unknown for that process?
 3. What is the meaning of various Gnome applications such as "gnome-pty-helper" and "gnomepager_applet"?

Many Thanks.