Hi Alice,
Here’s what I have my 8 year old does: clear off and wipe the table, fold and put away his laundry and the kitchen linens, clean his room, make his bed (including putting on new sheets), cleaning his zone (a certain area in the house-for him it’s the stairs and baby toys but could be anywhere that needs 1-2 time daily straightening), drys dishes, vacuums the living room/hallway, cleans up the dog poop in the yard, dusts, straightens the games/puzzle area. Some of these are only once a week and some are daily.
My 5 year old: empties the dishwasher, folds and puts away his clothes and the baby’s bibs, cleans his room, makes his bed (needs help with changing the fitted sheet), keeps the tubberware cabinet and plate cabinet straightened (his zone-the plates/cups are in a low cabinet), waters our plants, empties the house trash baskets into the kitchen garbage (the 9 year old takes it out to the big bin), checks mail (someone walks with him).
They both help me wash walls, baseboards, vents/intakes, hang clothes on the lines in the summer, cleaning the toys off the lawn before it’s mowed by the oldest 2, clean out the van of toys/garbage.
As far as how to teach them, I would pick one chore and have them watch you. Then they do it with you. Then they do it while you watch. Then they do it alone and you check afterward. Make it as simple as possible. Make sure to explain all the steps (ie does washing dishes include washing the sink down afterwards?).
For when, I would choose the time of day when you would be least rushed so you could give him the time he needs to learn.
HTH,Rebecca