For every pint of apple 'juice' you need a pound of sugar. Put them together in your jam pan and heat gently stirring regularly until the sugar has dissolved. Bring the mixture up to a rolling boil and test for set. I find it worth using a jam thermometer to see if it's reached 'setting point' before it's worth testing for a set. You need to put a teaspoon of the mixture onto a cold plate and pop it in the fridge for a few minutes. If the jelly wrinkles when you push a finger across it it is ready, if you just get a wet finger it is not! Jelly usually needs skimming as it gets very frothy. The froth tastes OK but it doesn't look pretty. Pot the jelly in warm sterilised jars before it cools, add a wax circle and a lid. Label when cold (otherwise you'll find the label difficult to remove when you recycle the jars next time around).
You can throw in chopped herbs to make say, mint jelly, but you need a surprising amount to make a real impression, and there wasn't enough mint or sage worth using left in my garden. The advantage of not adding anything is that you can use this jelly as an accompaniment to any roast meat, but it is also delicious on a piece of bread and butter - or on a drop scone was how my granny served it!