Wash it, pour boiling water over it, put hot jam or other preserves inside, it will hold all winter. Just make sure the lid is concaved when the jam cools down - that means it seals well.
I think the boiling water would also be to help sanitize the container, but yeah, I've always boiled the container with the lid on but loose after putting the contents in and closing while hot to get the container sealed.
The hot water is to kill bacteria, of course you remove the water before you put the jam in. I have apple jam from 2022 canned using this method and it still holds, no mold and good taste.
I'm wodnering what seems so odd in this procedure because that's how I've been taught to do it