Powers of ten: Exp
The Exp key means "times ten to the power of". For 5 times 10 to the 3, type 5, press 
, and type 3. Now press 
. Then type 4, press , and for a negative exponent press 
right after it, then type 3. Press 
. The answer is 1'250'000.. The small marks on the display separate the thousands.