A person who is blowing shofar, whether in shul or for people who cannot make it to shul, has an obligation to ensure that he is familiar with all the halachos of shofar so that the people he is blowing for will fulfill their obligation according to Shulchon Aruch. This brief synopsis is not a substitute for that requirement; however, we will mention a couple of halachos: It is important to ascertain that the shofar is indeed kosher, and that there are no cracks that may invalidate it. Sometimes even a small crack can invalidate the shofar. There is a required length for each of the kolos, the different types of blasts that have to be blown. The blast mentioned explicitly in Torah to be blown on Rosh Hashana is a teruah. This blast must be blown three times. However, the definition of the Torah expression "teruah" is unclear. It can refer to either the shevarim, or the shevarim-teruah, or the blast known today as teruah. Due to this doubt, we blow all three: shevarim, teruah and shevarim-teruah - and each of these three blasts are blown three times. In addition, each one of those blasts must be introduced with a tekiah and followed by another tekiah. Thus we blow: tekiah,shevarim-teruah, tekiah three times; tekiah, shevarim, tekiah three times, and tekiah, teruah, tekiah three times. The Shulchon Aruch calls a short blast a terumit, a very short sound. There are two opinions in Halacha as to the length of the blasts. According to the accepted opinion, a teruah is nine terumiten and a shevarim is three short blasts, each one consisting of three terumiten. A tekiah changes in length according to whether there is a shevarim, a teruah, or a shevarim-teruah in the middle. In other words, a tekiah is always the length of that blast which is in the middle, shevarim, teruah, or shevarim-teruah. A shevarim-teruah is normally blown in one breath.