This is step down Module. Using this module you can descrease the input voltage to a desired value. Like 12v to 5v, 24v to 5v etc. You can use this module to run arduinos feom 12v or 24v directy. You can power your mobiles from 12 or 24c battery using this module.
LM2596 DC-DC Step Down Voltage Control Circuit, 4-40v to 3-35v Module Board
Input Voltage - 4.5v to 40v
Output Voltage- 3 to 35v
Least Count - 0.1v
Rated current- 2-3A max
As its a step dowm module you get lower voltage from the input voltage.