The thumb rest is located in the back of the clarinet.
just put your thumb on the whole, that's on the first section of the clarinet.
Thumb and first top hole
The fingering for a c minor is thumb and first three
Hold down register key and cover thumb hole.
1st and easiest E on the clarient is thumb and first hole
You put your left thumb on the left thumb hole, and the next two top holes NOT THE REGISTER KEY OR THE A KEY
To keep your clarinet in good shape, you will need to purchase a few things. You will need cork grease, a cleaner that goes through the clarinet(so it gets all the saliva), a thumb rest(its rubbery and usually black) for your thumb so it doesnt go numb and a reed gaurd(so it keeps your reed in shape).
Cover all 3 (left hand) holes but also make sure that you cover the thumb hole at the back of the clarinet
B# is the same as C. So low C would be all fingers down, low E key and the bottom thumb key (if your bass clarinet has a low C) Middle C is thumb and 1st 3 fingers Upper C is thumb, register key, all 6 fingers down plus the bottom C key (on either hand) High C is thumb and register key (Super C is thumb, register key and index fingers)
C is just the top three fingers of your left hand down with your thumb on the back.
Yes you can its like low F but with your thumb key.