I would recommend that you read one of David Reed's books (see link). He explains the basics quite well.

Here's a pic of our dry-stacked stone wall:

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We had the wall done by a contractor, but it could have been a DIY project. We did lay the patio by ourselves after paying the contractor to grade the base and spread the crusher run. The wall is 3' tall and leans back a little for every foot of height. It is set on compacted crusher run.

Here is a link that might be useful: David Reed

Six INCHES? No, you don't need mortar or a base, or at least you wouldn't in my climate (zone 8). If you do use a base, heed the advice of Botann, above. Or you can use sand, but again, use sharp sand, not the one with rounded particles.

The question that determines whether or not to do a base has to do with what happens if you get frost heave or any sinkage. How difficult will it be to repair the wall and do you want to be bothered with that? Me, on such a small wall, I'd far rather have to do some spot repairs from time to time than mess with gravel and mortar to build it.

But definitely, there are some great books out there on building with stone.

Is this wall going to be a retaining wall, or free standing?

KarinL

I have found that the keys to a dry stack wall are keeping the courses level and using gravel (57 stone/crusher run) on the back side to keep the rocks stable and level. Fieldstone should be fine for a 6" high wall and no base is required. There are some good instructions on the net. You will just need a small trench to put the top of the first course at ground level.

If you use mortar then it's no longer a dry stacked wall. It's a mortared wall.

6" is totally doable. *snerk*

(sorry. I must be chaneling a certain deviant designer...)

You do understand that this seriously challenges my claim to the World's Smallest Retaining Wall. Mine is about 12" high, and three feet long. It's been there for at least five years, or since I put in the brick edging for the bed, and the dry laid stone path extension that runs underneath it. I"m not even sure I bothered with burying much of the first course.

Unless it's a very long wall, just pile them up.

... what KarinL said. All of it.

Spazzcat. Very nice! There is a book by Barbra Pleasent called Stone Gardening. I recomend this also as well as the one mentioned above. Well written and takes out the doubt of how to build stone walls, patios and paths etc... karinl nails it for this type of wall. Once you start using stone in garden design you will find many more uses for it. Get creative!