When do you downshift in a stick shift car?

Question

when is it necessary to downshift (at what decreasing speeds)? if you are going 40 mph and you need to slow down to 25 mph what exactally do you do? please be spicific

Answer 1

"and also. if you are in neutral, are you able to shift into second gear without messing anything up or being illogical?"

You may shift into any gear at any speed - but you want to select a gear that is appropriate for the speed you're going.  

Like if you're slowing on approach to a traffic light that turns green before you get there - no need to stop completely and put it in first.  Second is fine.

Answer 2

Common sense!!

Answer 3

Let off the gas, gradually apply brake, downshift into the next lowest gear.