All yeasts have a a published limit, EC-1118 for instance is listed at 18% ABV. Once the yeast has converted enough sugar into alcohol for the ABV to reach 18%, the yeast begins to die off from alcohol toxicity, so it sort of works itself to death. If you look up the yeasts you plan to use, you will find their ABV limits, some are as low as 12%, so we have to select properly in order to have the yeast function to completion.
Wine making can be similar to baking, there are just a few caveats, one being sugar additions. If you can use a hydrometer, you can easily read how much sugar you have and therefore how much alcohol you can produce if it's all converted. If you have enough sugar present to produce 8% ABV, and you want 12% ABV, a simple calculator like Fermcalc (
http://www.fermcalc.com/FermCalcJS.html ) will easily tell you how much sugar to add. Once all the sugar has been fermented out, and the wine is dry and stabilized with sulfite and sorbate, we can add sugar back to the wine to make it sweeter, without fear of fermentation re-starting.