If you don't have any special juicing equipment and you are going to do it with pan..there is not much recipe to follow.
Put black currants into pan with a drop of water at the bottom and lid on..slowly 'stew' until the berries have collapsed in the heat. Pour berries into sieve to separate juices or into muslin bag let them drain.
And that's it..all done..you can use it unsweetened as it is...sweeten it as you 'go'..or return the juices into pan, heat it up again and add lot of sugar..as much as the liquid is able to disolve so it comes almost syryp like, bottle it and done. The last version will store best..unsweetenened will last couple weeks in fridge or for longer storage you need to freeze it. You can freeze the sweet version too.
The left over bit from berries alway have quite a lot of flavour still left in them..you can use them by adding into pies and cakes..or if you choose, 'rinse' them again and 'squeeze' bit more out of them to use up first as black currant drink.. ;)
Any 'washed up' left overs you can be fed for chickens if you or somebody else you know have any.