I pitched my yeast last night at about 7 o’clock, but when I looked this morning I didn’t see anything happening yet. Did I do something wrong?
This probably isn’t enough information to diagnose your exact problem, but at least let me give you some of the more common things which could be going on here.
The most likely scenario is that your beer is indeed fermenting very well at the moment, but the level of CO2 has not yet reached the saturation point, which means it all stays in the beer, which in turn means that your beer doesn’t look like it’s fermenting. Carefully give your fermenter a good stern shake to see if it suddenly foams up. Chances are it will, in which case we’ve confirmed the above.
If you were using dry yeast, you can make your beer start fermenting faster by using two packages of yeast instead of one (which I do all the time), and also by making sure to rehydrate your yeast before using it. Good wort aeration is also important here. If it was liquid yeast you were using, then make sure you pitch a good healthy and large starter. And proper aeration is far more important with liquid yeast than it is with dry.
There is also a small chance that your beers have already completed fermenting. In 12 hours that’s unlikely, but in 24 hours it certainly isn’t unheard of. In fact, the Cooper’s kit in the gold foil which I’ve used can finish fermenting within 24 to 30 hours of having been pitched. Carefully shake the fermenter to see if you can raise a fizz. If so, then maybe it’s already done.
Yet another possibility is that you pitched the yeast when the wort was too hot, and thus killed the yeast. Make sure you have a reliable thermometer (the floating ones common in homebrew shops aren’t reliable), and make sure you stir the wort well to mix properly. Above 100F/40C is not healthy for your yeast.