user63786: First of all,here's the datasheet of the 4 digit 7 segment display that I'm using:
http://www.kingbrightusa.com/images/catalog/SPEC/ca56-11ewa.pdf
How can I make a counter or a clock out of this particular led display,considering the fact that I don't have enough digital pins to manipulate led's pins?

user42539: Only need 4, or 5 pins; SCK (D13), MOSI (D11), slave select (D10).
Maybe PWM (D9) for brightness.
D12 not used, but is tied up as part of SPI bus.
Connect the Anodes to +5.
Connect the cathodes, with a current limit resistor per cathode, to the outputs of 4 TPIC6C595, or TPIC6B595. 
For the resistor, assume worst case voltage drop of 2V and 20mA current draw:
(5V - 2V)/.02A = 150 phm.
Use a PWM output pin to drive the OE/ pin of the '595s for brightness control.
Then shift data into the daisychained shift registers as an update is needed.
byte dataMap[] = {
0b00111111, // 0 with bits representing DP,g,f,e,d,c,b,a
0b00000110, // 1
0b01011011, // 2
// etc
};

where segments are layed at as
   a
f     b
   g
e     c
   d      DP or colon

then call the array in loop(), make it a function if you want.
digitalWrite (ssPin, LOW); // D10 on Uno, used as Latch signal
for (x = 0; x <4; x=x+1){
SPI.transfer (mapArray[digit0]); // digit0 value mapped to segments
SPI.transfer (mapArray[digit1]);
SPI.transfer (mapArray[digit2]);
SPI.transfer (mapArray[digit3]);
}
digitalWrite (ssPin, LOW); // outputs update on this rising edge

I wonder where DP5, DP6, which make the colon, are? I don't see them in the pinout.

63786: <p>First of all,here's the datasheet of the 4 digit 7 segment display that I'm using:
<a href="http://www.kingbrightusa.com/images/catalog/SPEC/ca56-11ewa.pdf" rel="nofollow noreferrer">http://www.kingbrightusa.com/images/catalog/SPEC/ca56-11ewa.pdf</a></p>

<p>How can I make a counter or a clock out of this particular led display,considering the fact that I don't have enough digital pins to manipulate led's pins?</p>
 42539: <p>Only need 4, or 5 pins; SCK (D13), MOSI (D11), slave select (D10).
Maybe PWM (D9) for brightness.
D12 not used, but is tied up as part of SPI bus.</p>

<p>Connect the Anodes to +5.</p>

<p>Connect the cathodes, with a current limit resistor per cathode, to the outputs of 4 TPIC6C595, or TPIC6B595. </p>

<p>For the resistor, assume worst case voltage drop of 2V and 20mA current draw:
(5V - 2V)/.02A = 150 phm.</p>

<p>Use a PWM output pin to drive the OE/ pin of the '595s for brightness control.</p>

<p>Then shift data into the daisychained shift registers as an update is needed.</p>

<pre><code>byte dataMap[] = {
0b00111111, // 0 with bits representing DP,g,f,e,d,c,b,a
0b00000110, // 1
0b01011011, // 2
// etc
};
</code></pre>

<p>where segments are layed at as</p>

<pre><code>   a
f     b
   g
e     c
   d      DP or colon
</code></pre>

<p>then call the array in loop(), make it a function if you want.</p>

<pre><code>digitalWrite (ssPin, LOW); // D10 on Uno, used as Latch signal
for (x = 0; x &lt;4; x=x+1){
SPI.transfer (mapArray[digit0]); // digit0 value mapped to segments
SPI.transfer (mapArray[digit1]);
SPI.transfer (mapArray[digit2]);
SPI.transfer (mapArray[digit3]);
}
digitalWrite (ssPin, LOW); // outputs update on this rising edge
</code></pre>

<p>I wonder where DP5, DP6, which make the colon, are? I don't see them in the pinout.</p>
