Turn on the heat to medium-high (I use 7 on an induction cooker). Add the oil and let it heat up- it will take a few minutes. Either use a thermometer to check that the oil is 190C (380F) or toss a few kernels in to check that they pop. (If they burn the oil is obviously too hot- Popcorn burns easily FYI) (I have no food thermometer so I use the latter method)
Once the oil is hot enough, turn off the heat and remove the popped corn.
Put the rest of the kernels in and CLOSE THE POT, placing it back on the stove (so you don't get hit in the face by a flying kernel or oil). Turn the heat back to medium. Leave the lid a little ajar so the steam can escape, if not you get soggy popcorn. I like to have the hole in the lid further away from me to minimise the risk of getting spattered by oil. Give the pot a gentle shake to make sure the kernels are nicely distributed.
You'll hear the kernels start popping, which is great fun- shake the pot slightly again to make sure all the kernels are getting heated up evenly. Keep the heat on till the popping slows to 1 pop every 2-3 seconds.
Uncover, pour out the popcorn into a heat-proof bowl, sprinkle with salt and seasoning (see post above for seasoning ideas) to taste and give it a stir with the spatula to make sure all the kernels are coated. (Don't season in the hot pot or you'll season the pot not the popcorn)
Best eaten right away but I've kept it for several days in an air-tight container.