user2955: I'm rather disappointed because I just bought arduino and I am unable to upload any projects. The error I get is:
avrdude: ser_open(): can't open device "\\.\COM3": Časový limit semaforu vypršel.

Can be translated as:
avrdude: ser_open(): can't open device "\\.\COM3": Semaphore time out

Am I expected to brute-force all available ports to see which one is reserved for arduino? How can I, on Windows 7, quickly determine which port to use given that the IDE for some reason can't do that for me.

user10794: You may have to install a device driver. There is a "drivers" directory in the IDE download with some in it. 
Example:

According to the readme.txt file:

With this version of Arduino a new all-in-one driver (with
  security signature for Windows 8) is supplied.
The old (deprecated) drivers are still available in the
  Old_Arduino_Drivers.zip


user13749: Start | Control Panel | System | Device Manager | Ports (COM & LTP).
Watch the list change as you plug / unplug the Arduino. The new port is the Arduino.

2955: <p>I'm rather disappointed because I just bought arduino and I am unable to upload any projects. The error I get is:</p>

<pre><code>avrdude: ser_open(): can't open device "\\.\COM3": Časový limit semaforu vypršel.
</code></pre>

<p>Can be translated as:</p>

<pre><code>avrdude: ser_open(): can't open device "\\.\COM3": Semaphore time out
</code></pre>

<p>Am I expected to brute-force all available ports to see which one is reserved for arduino? How can I, on Windows 7, quickly determine which port to use given that the IDE for some reason can't do that for me.</p>
 10794: <p>You may have to install a device driver. There is a "drivers" directory in the IDE download with some in it. </p>

<p>Example:</p>

<p><a href="https://i.stack.imgur.com/VffAl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VffAl.png" alt="Windows drivers"></a></p>

<p>According to the readme.txt file:</p>

<blockquote>
  <p>With this version of Arduino a new all-in-one driver (with
  security signature for Windows 8) is supplied.</p>
  
  <p>The old (deprecated) drivers are still available in the
  Old_Arduino_Drivers.zip</p>
</blockquote>
 13749: <p>Start | Control Panel | System | Device Manager | Ports (COM &amp; LTP).</p>

<p>Watch the list change as you plug / unplug the Arduino. The new port is the Arduino.</p>
