The big ones (heads of cabbage) you cut in half, the smaller ones go into the barrel whole. You’re supposed to cut out the center at the stump and fill it with salt. Also add several grains of rice or corn to the brine to make it extra fizzy. People who add sugar should be neutered.
P.S: Every other day you should drain the brine and pour it in again to avoid stratification.
p.p.s: You may add cellery root or carrots (but don’t overdo it, strictly for flavor). Also, a small weight on top will help keep the cabbage submerged. That’s it, enjoy your sauerkraut.