The Combustion Turbine
Natural gas is mixed with air and burned in the combustion chamber to create the high pressure gasses needed to spin a turbine. This part of the plant is a single cycle, combustion turbine. These are sometimes called CTs. CTs are normally designed to meet peak loads.

The Combined Cycle Plant
A combined cycle power plant is a dual cycle plant. The "2nd" part of the combined cycle is a heat recovery unit. It takes advantage of the energy in the exhaust gasses to create steam. The steam spins a steam turbine to generate additional electricity. The combined cycle plants are normally designed to meet base and intermediate loads.