You put enough vegetable oil in a frying pan (one that has a lid) to cover the bottom of the pan, then you pour in the popcorn kernels, starting it on medium high or so, but adjusting depending on how fast the kernels pop. Make sure the lid is on so they don't fly out and burn you. Watch the corn, and listen to it as it pops. When the space between pops slows down a lot, you want to remove it from the heat and dumped the popped kernels in a paper bag (like the kind they used to use at grocery stores, double-bagged if possible). It helps to soak up some of the excess oil, but you can use a large metal bowl if that is all you have. Salt to taste.
Pop more pans-full as needed, and then when you have it all done, you melt some butter in the still-hot pan (depending on how much popcorn you made). Pour it over the popcorn, and then shake it up quickly, holding the bag closed, to distribute the butter evenly. (If using a metal bowl, mix quickly spoons or with clean hands (they will get very greasy and will have to be washed again). Then taste it and see if it needs more butter. You'll get the hang of how much to pop for your family, and how much butter to use for that amount quickly.