user9956: I created a shield for Arduino on a soldering board. The next step shall be to implement the circuit on a PCB. I'm new to this, so I'd like to know what the basic steps in designing a PCB are. 
More specifically, 

What software do I use for this? Is free software sufficient, or do I get substantially more value from a commercial package? 
Can I have a single PCB printed by a commercial provider, or are there minimum quantities? What is the approximate cost for a shield-sized PCB in a small quantity - is it in the tens, or rather in the hundreds of bucks? 

Of course, any pointers to good tutorials on the Web will be appreciated,  too! 

user4143: 
What software do I use for this? Is free software sufficient, or do I get substantially more value from a commercial package? 

There are plenty of good free ones, or free versions of commercial ones. Use the one that best suits your way of working - they are all different, try some out and find out which you like best.  I use a free one for all my work (but then I am a FOSS junkie).

Can I have a single PCB printed by a commercial provider, or are there minimum quantities? What is the approximate cost for a shield-sized PCB in a small quantity - is it in the tens, or rather in the hundreds of bucks?

Generally, no.  It'd be just too costly.  There are small quantity houses around though, and I often use iTead for my prototyping, since they will do batches of just 10 boards at a reasonable cost.
The basic steps in designing a PCB though are:

Design it as a schematic
Lay it out as a PCB design
Get a prototype made
Build it
Correct the mistakes
Go back to 3

If you only want one circuit and it is a pretty simple one you might want to give making the PCB yourself a go - it's quite rewarding and if nothing else gives you good insights into PCB design requirements and how best to lay out a PCB and the tracks for a good reliable etch.  If you have a laser printer the Toner Transfer method of home PCB production is good.

user2881: Software packages are, amongst others

Fritzing (more target at beginners)
Eagle (free for board of size 100 x 80 mm (4 x 3.2 inches)).
KiCad (open source)

Companies that make you pcb in small quantities are e.g.

OSHPark
seeedstudio
Dirt Cheap Dirty Boards

I personally create my own double layer PCBs at home. I first started with the toner-transfer method, but now use photo lithography. I etch in Hydrochloric acid and hydrogen-peroxide. I can have a finished board in 1-2 hours, instead of having to wait a week or so. Great learning experience.

9956: <p>I created a shield for Arduino on a soldering board. The next step shall be to implement the circuit on a PCB. I'm new to this, so I'd like to know what the basic steps in designing a PCB are. </p>

<p>More specifically, </p>

<ol>
<li><p>What software do I use for this? Is free software sufficient, or do I get substantially more value from a commercial package? </p></li>
<li><p>Can I have a single PCB printed by a commercial provider, or are there minimum quantities? What is the approximate cost for a shield-sized PCB in a small quantity - is it in the tens, or rather in the hundreds of bucks? </p></li>
</ol>

<p>Of course, any pointers to good tutorials on the Web will be appreciated,  too! </p>
 4143: <blockquote>
  <p>What software do I use for this? Is free software sufficient, or do I get substantially more value from a commercial package? </p>
</blockquote>

<p>There are plenty of good free ones, or free versions of commercial ones. Use the one that best suits your way of working - they are all different, try some out and find out which you like best.  I use a free one for all my work (but then I am a FOSS junkie).</p>

<blockquote>
  <p>Can I have a single PCB printed by a commercial provider, or are there minimum quantities? What is the approximate cost for a shield-sized PCB in a small quantity - is it in the tens, or rather in the hundreds of bucks?</p>
</blockquote>

<p>Generally, no.  It'd be just too costly.  There are small quantity houses around though, and I often use iTead for my prototyping, since they will do batches of just 10 boards at a reasonable cost.</p>

<p>The basic steps in designing a PCB though are:</p>

<ol>
<li>Design it as a schematic</li>
<li>Lay it out as a PCB design</li>
<li>Get a prototype made</li>
<li>Build it</li>
<li>Correct the mistakes</li>
<li>Go back to 3</li>
</ol>

<p>If you only want one circuit and it is a pretty simple one you might want to give making the PCB yourself a go - it's quite rewarding and if nothing else gives you good insights into PCB design requirements and how best to lay out a PCB and the tracks for a good reliable etch.  If you have a laser printer the <a href="http://hacking.majenko.co.uk/toner-transfer-etching-part-1-designing-the-circuit" rel="nofollow">Toner Transfer</a> method of home PCB production is good.</p>
 2881: <p>Software packages are, amongst others</p>

<ul>
<li><a href="http://fritzing.org/home/" rel="nofollow">Fritzing</a> (more target at beginners)</li>
<li><a href="http://www.cadsoftusa.com/download-eagle/freeware/" rel="nofollow">Eagle</a> (free for board of size 100 x 80 mm (4 x 3.2 inches)).</li>
<li><a href="http://www.kicad-pcb.org/display/KICAD/KiCad+EDA+Software+Suite" rel="nofollow">KiCad</a> (open source)</li>
</ul>

<p>Companies that make you pcb in small quantities are e.g.</p>

<ul>
<li><a href="https://oshpark.com/" rel="nofollow">OSHPark</a></li>
<li><a href="https://www.seeedstudio.com/service/index.php?r=pcb" rel="nofollow">seeedstudio</a></li>
<li><a href="http://dirtypcbs.com/" rel="nofollow">Dirt Cheap Dirty Boards</a></li>
</ul>

<p>I personally create my own double layer PCBs at home. I first started with the toner-transfer method, but now use photo lithography. I etch in Hydrochloric acid and hydrogen-peroxide. I can have a finished board in 1-2 hours, instead of having to wait a week or so. Great learning experience.</p>
