I would also suggest the two boards here at Craftster
that deal with polymer clay.
And there's also my website which is a huge online polymer clay "encyclopedia"
of lessons, explanations, examples, troubleshooting, etc... here is a link to the Table of Contents
(scroll all the way
Polymer seems to be what every website takes me to. . .
There are many things that can be made with "air-dry" clays as well as with polymer clays but mostly just the "sculptural" ones. Polymer clays can do loads more
things than just sculptural things.
As for your specific questions,
really good tutorial for beginners
Well, since there are many-many-many techniques in the field of polymer clay, and many different things that can be made with it, there are thousands of tutorials online that you might be interested in.
You might want to start with just a few of the posts I've written before though specifically for beginners to polymer clay:http://www.craftster.org/forum/index.php?topic=265189.msg2978691#msg2978691http://www.craftster.org/forum/index.php?topic=73664.msg1638472#msg1638472
and this page at my site has a section on Adult Beginners
And since I see a sewing machine as your icon, you might be interested in making buttons from polymer clay too (polymer clay can also be sewn, and made to look like fabric and fabric techniques, etc., but that's jumping ahead):http://www.glassattic.com/polymer/buttons.htm
what types of clay are typically used for necklace pendants?
Clayers use whichever brand and line of polymer clay suits their individual needs and the needs of a particular piece (though beginners and others may just stick with the first brand they try too). The most important things to remember about choosing a brand/line are that Sculpey III (and Super-Sculpey flesh, and original Sculpey) will be weak after baking in any places they're not thick and rounded or they're projecting, so they can break... and that clayers with hot hands or hot environments will probably want to use Kato Polyclay or FimoClassic.
Here is my page specifically on pendants, if you're interested:http://www.glassattic.com/polymer/pendants_cording.htm
(...that page won't cover the many polymer techniques that can be used to make the patterns, colors, etc, for pendants, just the basic ways pendants are made... the other things will be on their own pages)
...also, if you are not stamping a design into the clay, can you layer polymer?
You can layer polymer clay in all kinds of ways and for all kinds of reasons, so not sure what you're asking about --and stamping into or onto polymer clay is only one of the many things that can be done with it. Could you reply again and be a bit more specific about what you have in mind?