It depends,
their Mama usually shows them. Seems most cats I know do OK and don't need help.
My advice is keep them in a small area with a small litter box they can get into. If they show ANY signs of going outside of the litter box, immediately put them in it, and they get the picture then.
Also, if the do 'go' outside the box, you can put the droppings in the box as a clue of 'this is the right place'.
I never ceased to be amazed at how fast kitties pick up the litterbox concept. This past spring, after 3 months of effort, I captured a 6 month old feral female kitten who had turned up in my garden. She'd clearly never been touched by a human or inside a house before (though by this time we'd gotten her pretty clear on the connection between humans and food). Had to keep her in the house overnight to get to her spaying appointment the next morning (we caught her just in time -- two tomcats had just appeared in the garden the day before!). She had the run of a couple of hallways, a carpeted staircase, and a large bathroom with a litterbox in it. She used the litterbox.