Just by applying some techniques, you can ferment your home-brew to your desired alcohol content ranging 5 - 12% ABV (alcohol by volume) even more.
But if you plan to stabilize and leave to age your brew for longer period of time the ideal preservation alcohol by volume ABV is 12.3%.
One of the easiest ways of eliminating the guessing game is using this simple hydrometer shown below. It even lets you measure the BRIX (sugar content) of your must (fermenting juice).
The fermentation locks or airlocks as shown on the below disply are a device used in brewing that allows carbon dioxide released during fermentation to escape the fermenter, while not allowing air to enter the fermenter, thus avoiding oxidation.
As shown on the display, you may also improvise and use balloons with small holes on top of your bottle, which more or less will deliver the same purpose as the airlocks.