user-1: Question
As far as I know each I/O pin has to keep around 20mA, what are the consequences of going higher or lower? But if I am using all I/O pins is there a maximum current value I should keep in mind? For example, the sum of all currents in all pins should not be greater than 100mA.

user22914: The power limits per pin and per chip are listed for each model (based on the Atmel chip).  You can look up the Atmel chip number and see the power ratings.  For example, the chip may have a maximum of 40mA per pin, but a total of 200mA for everything on the chip. These numbers are just examples. The actual numbers depend on which Arduino and which chip you are talkng about.
Remember that microcontroller chips are NOT designed to SWITCH any significant amount of power. That is NOT the job of the microcontroller. Its job is to CONTROL external devices (transistors, thyristors,SSR, relays, etc.) which do the actual "heavy lifting" of switching larger amounts of power.
Your last question really does not make any sense. Can you clarify it?
VCC is the name of the main power bus and input to the microcontroller chip. It may or may not be 5V depending on which Arduino you are talking about. The older ones were 5V, but newer chips (including those used in Arduino) are tending more to 3.3V.

user7734: This comes up as first result when Googling your question:

And can be confirmed by page 313 and 314 of the datasheet:

To know where each pin is connected to (on the Arduino Uno) you can look the official (messy) schematic.
I provide an excerpt below that shows the Vin and 5V pins at the headers, and the power barrel connection. 

If you want to control a 12V motor or a 12V LED strip or other DC loads you can use the following (which is also easy to find using Google):
*Note that your 12V Gnd and Arduino Gnd have to be connected.

simulate this circuit – Schematic created using CircuitLab

-1: <h3>Question</h3>

<p>As far as I know each I/O pin has to keep around 20mA, what are the consequences of going higher or lower? But if I am using all I/O pins is there a maximum current value I should keep in mind? For example, the sum of all currents in all pins should not be greater than 100mA.</p>
 22914: <p>The power limits per pin and per chip are listed for each model (based on the Atmel chip).  You can look up the Atmel chip number and see the power ratings.  For example, the chip may have a maximum of 40mA per pin, but a total of 200mA for everything on the chip. These numbers are just examples. The actual numbers depend on which Arduino and which chip you are talkng about.</p>

<p>Remember that microcontroller chips are NOT designed to SWITCH any significant amount of power. That is NOT the job of the microcontroller. Its job is to CONTROL external devices (transistors, thyristors,SSR, relays, etc.) which do the actual "heavy lifting" of switching larger amounts of power.</p>

<p>Your last question really does not make any sense. Can you clarify it?</p>

<p>VCC is the name of the main power bus and input to the microcontroller chip. It may or may not be 5V depending on which Arduino you are talking about. The older ones were 5V, but newer chips (including those used in Arduino) are tending more to 3.3V.</p>
 7734: <p>This comes up as first result when Googling your question:</p>

<p><a href="https://i.stack.imgur.com/XL0p4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XL0p4.jpg" alt="enter image description here"></a></p>

<p>And can be confirmed by page 313 and 314 of the <a href="http://www.atmel.com/Images/Atmel-8271-8-bit-AVR-Microcontroller-ATmega48A-48PA-88A-88PA-168A-168PA-328-328P_datasheet_Complete.pdf" rel="nofollow noreferrer">datasheet</a>:</p>

<p><a href="https://i.stack.imgur.com/zJZgj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zJZgj.png" alt="enter image description here"></a></p>

<p>To know where each pin is connected to (on the Arduino Uno) you can look the official (messy) <a href="https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf" rel="nofollow noreferrer">schematic</a>.</p>

<p>I provide an excerpt below that shows the <strong>Vin</strong> and <strong>5V</strong> pins at the headers, and the power barrel connection. </p>

<p><a href="https://i.stack.imgur.com/kDojF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kDojF.png" alt="enter image description here"></a></p>

<p>If you want to control a 12V motor or a 12V LED strip or other DC loads you can use the following (which is also easy to find using Google):</p>

<p>*Note that your 12V Gnd and Arduino Gnd have to be connected.</p>



<p><img src="https://i.stack.imgur.com/urNHq.png" alt="schematic"></p>



<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2furNHq.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>
