This module has a multi-turn trimpot (potentiometer) that you can use to adjust the LM2596's output voltage. Since the trimpot has 25 turns of adjustment you can easily adjust the output of the module to exactly the voltage you need.
The simplest way to reduce the voltage of a DC supply voltage is to use a linear voltage regulator (LDO), but linear regulators step down voltage by dissipating the excess energy as heat and do not yield any current step up. Buck converters, on the other hand, can be remarkably efficient and provide a step up in current output. Buck converters are one of the best ways to provide a regulated voltage from a battery since they don't waste near as much energy in the process of dropping the input voltage as a linear regulator would waste.
As an example of the characteristics of this module, Addicore ran a test with a 15V supply input and the output of the module adjusted to 5V with a 100 ohm load connected on the output. The input current was 24.8 mA, while the output current was 47.84 mA. That is nearly double the input current. You won't ever see that happen with a linear voltage regulator. We were able to change the input supply voltage down to 6.5V before the output voltage started to dip below 5V. The output voltage was still 4.99V, even with the input supply voltage at 6V. As we were adjusting the input supply voltage, the output didn't waiver a bit until around the 6.5V mentioned before and we didn't have to adjust the trimpot at all for the LM2596 to maintain the same output voltage. That is a perfect example of why switching buck converters can be such a great way to convert DC voltages.
If you need to increase (step-up) a voltage consider using a boost converter such as MT3608 boost converter module.
IMPORTANT: This module has an on-board power indicator LED connected on the module's output. This LED has a 1k ohm resistor in series with it as a current limiting resistor. If you adjust the module for an output voltage over 12V we recommend removing the LED or swapping the 1k ohm resistor for a higher resistance to prevent the resistor from getting too hot and to protect the LED from damage.