The zeroth law of thermodynamics discusses thermal equilibrium, and in so doing, gives meaning to the term temperature. The first law describes the conservation of energy, and dictates that energy cannot be created nor destroyed. The second law says, in a variety ways, that no system can be 100% efficient, and as such, every system has losses.
If you are curious, the reason that there is a zeroth law is that it was developed decades after the first two, but precedes them in terms of scientific principle, in that it lays a foundation for further study. Rather than shift laws one and two up to two and three, it was decided that they be left alone, and that the new law be referred to as law zero. This was a great choice, because it gave scientists the opportunity to use the term "zeroth", and as a result, sound very intelligent.
In summary, law zero says there will be lunch, law one says that it will not be free, and law two says that actually, you have to tip.
