There are three main components in both the turbines. Gas turbine power plant has Compressor, Combustor Chamber and Turbine while steam turbine power plant have Condenser, Boiler and Turbine.
Driving source for gas turbine power plant is fast flowing combustion gasses while in steam turbine power plant driving source is high pressure steam.
In gas turbine power plant, compressor in take the air and provide it to combustion chamber at high pressure causing the increase in intensity of burning gasses. These gasses are used to run turbine.
Thermodynamic process use in gas turbine power plant is Brayton cycle while in steam turbine power plant uses Rankine cycle
Gas turbine power plant are simple in designing and does not need any boiler to operate while in steam turbine power plant fuel needed to heat water is cheap and required less space to install and can also be install at any place.
Gas turbine work at high pressure and high temperature this need highly precision component and exotic material which are very expensive to manufacturing while steam turbine power plant can pollutes atmosphere and have high initial cost.