There are several methods. The one already mentioned is most common.

I actually own several 3D cameras that are designed spicifically for the
purpose of creating 3d iimages.

But most of the time I use one digital camera and take pictures from 2
slightly different view points.

I'll assemble one of my orchid 3d's and post it on alt.bin.pict.orchids for
you to look at. It might take a little while for me to do this so I'll post
a message here when I get it done.

Good day,
Francis M