To say to your team "hi":
bind (key) say_team hi
Using the numpad is a bit harder. On the numpad, 1 is 'kp_end', 2 'kp_downarrow', 3 is 'kp_pgdn', 4 is 'kp_leftarrow', 5 is 'kp_5', 6 is 'kp_rightarrow', 7 is 'kp_home', 8 is 'kp_uparrow', 9 is 'kp_pgup', 0 is 'kp_ins', . is 'kp_del', the + is 'kp_plus', the - is 'kp_minus', the slash is 'kp_slash', and the * is just *.