Almost all non-alcoholic or alcohol free wines start life as a full-strength equivalent (8 - 15% ABV), however, how they end up without the alcohol can vary. Below is a summary of the three most commonly used methods to help you understand how these processes work.
Reverse Osmosis - channelling your GCSE Biology knowledge, you may remember that osmosis involves molecules passing between a permeable membrane. In the case of wine, water and ethanol pass through a filter, whilst other elements (eg. colour, tannin, etc) do not. The alcohol is then distilled off, with the resulting water then reintroduced to the elements that remained previously.
Vacuum Distillation - heating the wine in a vacuum, often using steam rather than a direct heat, reduces the temperature at which the volatile compounds (flavours, aromas, etc) are burned off. During this process, these elements are collected, before the same happens to the alcohol on a second pass. The desired elements are then reintroduced to produce the finished liquid.
Spinning Cone - not dissimilar to the above, bar the introduction of a centrifuge which uses a combination of spinning and static cones to separate out the elements contained within a wine (owing to their different densities) before bringing the ones you want back together again.