The technique was to first shovel in a "pad" of concrete, then set stones with the desired "faces" against the forms.  Temporary braces would hold them until I shoveled in more concrete to hold them permanently.

Then I'd roll up wads of wet newspaper and squish it in around the periphery of each stone.  This was to keep the concrete from oozing in and covering the face of the stone.

Note the 2x4 "cleats".  They held the two sides of the forms to a uniform 16" in width.  Baling wire also spanned and secured the forms.

The wire stayed in place after the cleats were removed.  It kept the forms stable so the next level above could be nailed to them.