IT (Initial Touch) means the strength with which you first hit the key.
(After Touch) means the pressure you apply to the key after you have pressed
PB (Pitch Bend) means - bending the pitch of the note.
You achieve this by using the 2nd expression pedal.
HPB (Horizontal Pitch
Bend) is exactly the same as PB, you control the extent of the "bend"
with the horizontal touch control of each key.
Bonney's Music School