Operating Voltage
Microcontroller boards need a supply voltage to power them on, usually between 5V and 12V. They have output voltage pins to supply power to connected components, which can be 5V or 3.3V or both. The operating voltage of a board is the voltage of the signal output on the pins to which components and other boards are connected to exchange data with, which can be 5V or 3.3V (but not both).
In electronics, VCC commonly stands for Voltage at the Common Collector. It represents the positive power supply voltage for circuits.
Modules and components almost always have the same supply and operating voltage.
It is very important to know the operating voltage of the board and each connected component. If a component with a 3.3V operating voltage is connected to a board with a 5V operating voltage the component may burn out. If a component with a 5V operating voltage is connected to a board with a 3.3V operating voltage it may not work properly.
For example, an Arduino Nano can supply 5V or 3.3V to power components but has an operating voltage of 5V. So even if you connect a 3.3V component with the correct supply voltage it may still burn out because the signals from the Nano will be at 5V.
On the other hand an ESP32 can only supply 3.3V and has the same operating voltage. So all 3.3V components will work just fine but 5V components may need an alternative power supply, while the signal voltage may be sufficient.
If you must use a board and components with different operating voltages, you can use a level shifter. This is a circuit used to translate signals from one voltage level to another. Level shifters only work with digital signals, you cannot level shift analog signals. For some 3.3V components, the pins are 5V tolerant so a level shifter is not required.
Powering Modules and Components
When starting with building circuits we typically use breadboards. Modules and components are then supplied power directly from the output power pins on the board. You can get a breadboard compatible power supply module with a barrel jack connector that can be used to power modules and components separately using an AC to DC converter.
Current Drawn
Each microcontroller board is capable of supplying a maximum current and each connected component draws a certain amount of current. If the connected components together draw more current that the microcontroller board can supply the circuit may not work properly.
Common Ground
All power supplies, boards, and components that are connected to each other must have a common ground. While boards and connected components generally always have the same ground, mutliple boards exchanging data with each other may not always share a ground. This is especially important if two boards are exchaging data using UART or if a microcontroller and the connected components are powered by different sources.