the how and why of growing grain

so grain is most of the calories that people eat
and it is mainly that it is a mostly untended crop,
once you plant it, it comes up fast, way faster than the weeds (because the seeds have more energy in them than the weeds), and the grains block enough of the sun out that the weeds just don't grow that much.

so to get the grains to do what you want,
you have to plant them close enough to blot out the sun off the ground, but not so close as to take to much water and other things out of the ground and get a failure,
there is fairly wide range where grains will give you the same yield for a given area,
sets say for a specific kind of oat you can plant it anywhere from 3 inch centers to 6 inch centers with the same harvest numbers, any closer or further and you start to get less harvest.

as far as planting, most people just scatter the seeds mostly even and rake it in,
there are people that start grains in seed trays and replant out in the field when they get bigger, but that is mostly done if you have very few seeds to start with.
there is automated hardware that will plant it all at the correct depth and spacing, and I am not sure if you get a huge advantage from it...

after you plant it,
usually (at least historically) it is let be till harvest time,
it gets no weed removal or irrigation,
and that is why people can grow huge areas of it with relative ease

growing food trees only required harvest time...
growing wheat is likely the second best, it should take a somewhat healthy person about 6 weeks of work to feed a family of 5 for the year. you do need the land area to do this in, so that is why it was usually a rich persons food and not a slaves food.
growing potatoes gets you the most food for the area (at least for annuals), but takes way more effort to grow than the wheat.

as far as types of grain,
there are a few kinds that are popular,
oats, wheat, barley, corn, sorghum, millet, teff,

each one grows with it's own advantages for growing and for eating.
and if you are trying a survival garden, grains grown in the wet season is likely going to be second only to nut trees.