First, choose your recipe. Allow the wine to ferment to a Specific Gravity of 1.045. This will take about a week. Check the SG every day.
Fine the fermenting juice to obtain a clear product. Add 3 parts Brandy to 5 parts wine. The alcohol from the Brandy will kill the yeast, so there is no danger of exploding bottles.
Bottle the Port, leaving a slightly larger airspace than normal. Put the Port into storage.
Taste your Port in about a year. It is ready when the flavour is nice and smooth.