If you are using a thick-bottomed saucepan like a dutch oven then you just need to make sure the sugar dissolves. Then you can just stir from time to time. However, if you are using a thin-bottomed pan you have to stir continuously to make sure nothing burns. I did burn my last batch of apple jam just because I had so many that I decided to use the biggest pot I had and it did not have a thick bottom. Needless to say, the black layer of burnt apples and sugar broke apart into little pieces which penetrated the jam all through. You still can see the little black dots in the jars of my apple jam!