Transistors is the number of transistors on the chip. You can see that the number of transistors on a single chip has risen steadily over the years. Microns is the width, in microns, of the smallest wire on the chip. For comparison, a human hair is 100 microns thick. As the feature size on the chip goes down, the number of transistors rises.
Clock speed is the maximum rate that the chip can be clocked.
Clock speed will make more sense in the next section. In many cases the external data bus is the same width as the ALU, but not always. Modern CPUs can do so many different things that MIPS ratings lose a lot of their meaning, but you can get a general sense of the relative power of the CPUs from this column. The maximum clock speed is a function of the manufacturing process and delays within the chip. Modern processors can often execute at a rate of 2 instructions per clock cycle.