I'm not into kimchi (at least the chili pepper aspect that seems default) but I make sauerkraut somewhat regularly, not infrequently with some other stuff tossed in with the cabbage. Some research indicates that eating fermented vegetables might be a good thing for the present pandemic, so might as well if you enjoy them anyway.
Assuming moderately fresh cabbage, just split, cut out the core, slice thin, weigh carefully, mix in 1.5-2% by weight salt, stir it around with your clean hands and wait 30 minutes (or "massage it 30 minutes" for the "let's make this more work than it is" crowd) and then pack it into a jar unless you have a fancy crock. I fooled around with weighting it down with (clean) ceramic tiles to be "sort of like the ceramic weights in a proper fermentation crock" but have gone to "plastic bag full of brine" as a better weight. There should be no need to "make brine" (other than to fill that bag, if using) with fresh cabbage - all the water needed for the brine is in the cabbage when you start. (yes, I have seen other recipes that use brine, but I don't follow them. If you want to make real fermented dill pickles, you'll need brine, and I would too.) If the cabbage is old and dried out you might need to add water if it won't make enough brine on its own. You really pack it into the jar, (I have 7lbs in a gallon jar as I write this, with a little headspace for bubbling) and then the weights keep it from rising up above brine level when it gets going. I suspect not weighting it down might be part of KbD's need to add pickle-juice.
If the vegetables poke up above the liquid, they tend to mold, or get Kahm yeast. The container should be airlocked (the ferment makes CO2 and oxygen is problematic for causing various spoilage), but I'm down to plastic wrap and a rubber band (or using a mason jar lid and not cranking it down too hard - they will self vent, they do not need to be "cracked daily" as the same folks that make it too hard like do say.) Keep it in the dark unless you use an opaque crock, keep it in the basement or someplace cool-ish if you have one (unless you want to follow a co-worker's Korean Mother-in-Law's advice and bury the crock in the garden in the fall, and dig it up in spring.) Somewhere down in the 60's F or 15-20C is a good range - much above 75F and it's liable to be excessively soft/slimy and/or have off-flavors.
Food safety-wise, the stock quote is that there have been zero cases of food poisoning from fermented vegetables (that does not mean they can't go bad, but it does mean that evidently is not a subtle thing and you'll probably choose not to eat it.) I'm presently eating some that's been in the basement for ether a year and a half or two and a half years, though that is not ideal (it was lovely red/pink kraut, and now it's more brown than is appealing to look at) but it's not spoiled either. Better to eat it within 6 months, but I figure I'm no worse off an a scurvy-free German sailor a couple of years into a voyage. By 6 weeks or so it should be done and you can refrigerate for better long-term condition. If warmer (75F range) 3 weeks should do it. If you get something you enjoy after 3 days, that's fine, too, but the "full ferment" is far from over by that point. But given it's the height of summer in the Northern hemisphere, you may be better at 3 days if you don't have a cool basement/cellar.
The salt creates an environment where the lactic bacteria (no, not milk, don't... more web idiocy) that are naturally present are favored, and the lactic bacteria make lactic acid which makes the ferment unappealing to Bad Things such as botulism. Most US sources suggest 2% at a minimum, some German source go as low as 0.75% (but you'd better be pretty darn clean in your process for that.) Brine (not simply extracted from cabbage by the salt) complicates the math because you're bringing in water as well as salt with brine.
Some folks like seasoning with caraway seeds - I don't, though fennel seeds are fine by me. An amusing point is that I dislike cabbage cooked or fresh - sauering makes it into something I enjoy eating (but that's also part of the reason I don't sample mine early - that, and avoiding contamination of an ongoing ferment.)