Prepare a stomping pit
You can use a mortar pan or dig a hole about 1/2 shin deep. The wide range depends on how many people will work in the pit.

1.

Fill up the pit with soil and water 
Put soil and water into the stomping pit for at least 2-3 hours to brake down the hard soil & make it easier to mix

2.

Stomp until the soil break into small pieces & smooth

3.

 If the soil has too much clay in it, add sand to increase strength & reduce shrink rate that cause flaction in the brick. Keep stomping until they mixed well.

4.

Put chaff in the pit & keep stomping until the mixture are well mixed. 
To see if the mixture is ready -- Once you lifted your foot, the mud will slowly collapse but still left a print in the mud.

5.

 Wet the mold with water so the mud won't stuck inside the mold. Put the mold on dry & smoth surface. Fill the mixture into the mold. Make sure that every corner are full. Scrape off the extra mud. Slowly lift up the mold straightly and evenly. 

6.

 Let it lay flat for a few days. Flip it to the side. Make sure that the bricks are firm enough to flip. Let it dry compleatly  in about a week or longer depend on the weather. When it's dried, stack them up by leaving some gab between each brick to prevent the bricks from absorb back the humidity.  

7.