The best part of the Arduino is the Headers - this is the name of the two lines of sockets that line up with the edges of the circuit board.

These thin sockets allow you to plug wires into them. You can then connect those wires to all sorts of electronic parts like LEDs, displays, sensors, motors, and more!

For example, here's a future project you'll likely build, its an Arduino wired to a light up text display:

Those wires that are jumping between the display and the Arduino are called Jumper Wires, Jumpers, or sometimes Hook up Wires or even just Wires.

You can use fancy premium jumpers with rubber or plastic tips to make gripping them easy:

Or cut your own using 22 AWG Solid Core wire

And a pair of wire strippers

Header Sections

There are three groups of headers available:

Power Header

The power header is in the middle bottom. This header lets you connect to the power pins in order to borrow your power connection from the USB or DC jack and use that to drive motors, sensors, motors, anything you like.

You'll soon get very comfortable with these, but let's just introduce them for now and you can refer back when necessary

Starting from the right...

• Vin - This is connected to the power input from the DC Jack, so it is going to range from 7 V to 12 VDC, depending on what is plugged into the DC Jack. If the DC Jack is not powered, it will provide the 5V from the USB connection. Provides as much as the DC power supply can.
• GND - You get two of these here, they are the common ground connection for all power and data
• 5V - This is the clean regulated 5V power that the Arduino runs on, provided from the DC jack (if plugged in) or USB connection (if DC is not plugged in). Provides up to about 500mA current draw.
• 3.3V - This is a clean regulated 3.3V power, sometimes you'll need exactly this voltage for some sensors. Provides up to about 100mA current draw.
• Reset - This is the same pin connected to the reset button
• IOref - Used by shields to know what the IO voltage is. You can ignore this pin.
• Unnamed pin - Reserved for future use, don't connect to it!

Digital Pin Headers

The two digital pin headers are along the top. These are the digital inputs or outputs that you'll be using to control a relay, blink and LED, listen for switches or connect to more complex components. They use 5 Volts for 'high' signals, and 0 Volts for 'low' signals.

You'll soon get very comfortable with these, but let's just introduce them for now and you can refer back when necessary

Starting from the right...

The two pins labeled 0 (RX) and 1 (TX) are the two Serial pins that are used to send data to and from the Arduino to the USB-Serial translator chip. 

• Digital 2 through Digital 12 are normal every day digital pins. Some can do PWM (we'll talk about that later) and have a squiggly line next to them.
• Digital 13 is a little special because it is also connected to the L LED. You can use this pin without affecting the Arduino just be aware that the L LED will also blink at the same time.

And a few extra straggler pins:

• A spare power GND Ground pin
• AREF - Analog Reference pin. Used for advanced analog sensor reading (You'll learn about this later)
• Two unlabeled pins (the labels are on the bottom). These are the SDA and SCL pins, which are used for connecting I2C type sensors. They are connected inside the PCB to A5 and A4 We do not recommend usin these unless you have an I2C sensor (You'll learn about these later)

Analog Pin Headers

The analog input pins are special pins that can read sensors. You'll soon get your hands dirty with analog sensors, it'll be so much fun!

Each analog pin can read a voltage between 0 and 5 V (the same voltage used to power the Arduino.

Once you get advanced analog skills you can connect the ARef pin to a different voltage like 3.3V and direct the Arduino to use Aref as the max voltage, then you can get more precision. But we'll cover that some other day.

Shield Add-ons!

As you get more experience with Arduino you'll want to soup it up. Accessories for the Arduino are super popular and many plug into the headers. Normally these would be called "Daughter-cards" but in Arduino parlance they are refered to as shields. There are hundreds if not thousands of shields out there that add all sorts of capabilites that the native bare UNO cannot do. Here are a few of our most popular shields: