No need to disconnect the battery.
No need to connect clamp to chassis.
Its quite safe to charge with battery insitu. Just connect clamps to positive and negative terminals before switching on the charger.
You should disconnect the negative battery terminal if you are planning on charging it for a long time. If u dont you will cause damage to the alternator.
if you are jump starting a motor put the neg to a point on the engine block or lifting bracket. ( making sure it's a good & safe earth point ) the reason is the electric then goes through the starter more readily /easily than if it's attatched to the battery which will try to hog the power to charge it's self.
as said before though put on 'battery' to 'charge battery'