Im reading about rocket engines and I have a question about is it possible to use fuels in the form of gases than a liquid in a rocket engine?
Feasable: not really (at least not for power applications).
The main trick is energy density (per volume) - gases tend to be quite significantly less dense than liquids - and thus the tanks would need to be much larger and heavier - so they are commonly used in their condensed liquid form.
For small engines gases have been used - both as cold gas thrusters and in amateur experiments.
Yes, and it is currently being done on a few engines, notably SpaceX's Raptor engines. They run on liquid oxygen and liquid methane. These are run through turbopumps in two different mixture ratios, burning a small part of the fuel which spins the pumps and vaporizes the rest of the fuel. When they enter the combustion chamber they are both in gaseous form. This improves fuel mixing and therefore combustion efficiently, as gases mix faster than liquids. As such it is referred to as a "gas-gas" engine. Note however that the fuel is stored in liquid form, as it is much denser when liquid.
To complement the answer:
1 L contains 1141 g of liquid oxygen 1 L contains 1 g of gaseous oxygen (at 1ATM)
Of course you can compress it but the container will add more weight (highly undesirable).
But that's not over!
Rockets consume not only a lot of propellant, but they consume it fast.
A Saturn V consumes 18000 kg every second.
That would be 18143 m³ per second, about 20 olympic swimming pools. You can't force that much air in an engine.
For reference, a scuba diving tank is heavy and can hold a pressure of about 200 atm – one order of magnitude less than liquid oxygen.
You need a liquid to cool a large and hot combustion chamber efficiently. Ablative cooling has been used for smaller engines only. Heat transfer from the solid chamber walls to a gas is too small for cooling.
Burning gases is an aim.
Carrying fuel of maximum density is another.
Propellant density and thus increased propellan payload was (and is) of such interest that in the 1990s the use of "Slush Hydrogen" was propoesed - ex mix of Solid (!) and liquid Hydrogen which increased Hydrogen payload by about 20%. The problems proved to be considerable. A summary of the slush hydrogen technology program for the National Aero-Space Plane - NASA, 1995
Turning liquids into well mixed gaseous products is a major aim in rocket engines.
These photos illustrate the effort taken to do this:
Google Photos version here
The "injector" is the many many small holes lining the surface of the back wall of the combustion chamber.
As a bonus the channels for nozzle fuel cooling can be clearly seen.
Click image for higher resolution view:
Other answers have focused on the fact that you wouldn't want to run a rocket engine on gases because the tanks would be too large. One thing that hasn't been mentioned yet is the turbopumps.
Turbopumps consist of a turbine which runs on burned fuel and oxidiser. This runs a pump which pumps the liquid fuel from a low pressure tank to the high pressure needed for the combustion chamber. If the fuel were pumped in gaseous state, the pumping power requirements would be much, much higher. So the turbopumps would be much heavier, as well as using power which could otherwise be used in the main combustion chamber / exhaust nozzle.