Chop the potatoes, celery, carrots, and onions into bite-sized pieces. This means pieces between 1 and 2 cm (1/4 - 1/2 inch) across.
Put everything except the creamed corn and milk in a big pot. Add enough water to barely cover them.
Put the pot on the stove and heat it to boiling. Put the lid on so that it will heat up faster.
Turn the heat down to low and move the lid so that it is only mostly on. Boil the soup until the carrots are soft. Carrots cook the slowest, so everything else will be done by them. If the water stops boiling, turn the heat up slightly. If the pot boils over, turn the heat down slightly if possible. Otherwise, move the lid to cover less of the pot.
Stir in the creamed corn.
Heat the pot until it is barely boiling, with a few bubble popping. This is called a simmer.
Stir in the milk.
Heat the soup for 5 minutes on medium-low power. Don't let it boil, or the milk will burn. Stir regularly.
Notes:
I previously said to let it simmer for 5 minutes before adding the milk. This step is unnecessary.
I previously said to perform the final heating on lowest power. This took too long.