Wheel throwing takes time and a lot of practice. First start with a baseball sized lump of clay. Then slap it down on your bat. Cup your hands around the clay to center it and then once you have a smooth dome shape, put your thumb in the middle and press down until you are almost at the bottom. With your thumb still on the inside and fingers on the outside, slowly pull outwards then upwards. You can then shape it any way you want. Once you are done, you can use your shammy to smooth the edge.
I have had a lot of practice, so centering the clay is easy but I always have a hard time making the pot tall.