Summarize this article in one sentence.
Open the can of pineapple and pour the fruit and the juice into a large saucepan. Then add the 2 cups (480 ml) of sugar and stir with a large spoon to combine. Heat the pineapple and sugar mixture over medium heat. Stir regularly to ensure equal heating. Keep stirring until the mixture reaches a boil. Once the mixture has reached a boil, set a timer for 20 minutes and stir the jam constantly. As you reach the 20 minute mark, you should notice that the jam has started to thicken considerably. After 20 minutes, spoon up some of the mixture and assess whether it has reached the thickness and consistency of jam. If it is still thin or runny, keep cooking until it has reached an optimal level of thickness. You can also stick a thermometer into the jam. If it has reached 220 degrees F (104 degrees C), it has reached the jelling stage and should be ready.

Summary:
Combine pineapple and sugar in a saucepan. Bring the mixture to a boil. Cook for 20 minutes. Take the jam off the stove when completely thickened.