Gamma-rays are a form of electromagnetic radiation, just like radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves.
Gamma-rays can be used to treat cancer, and gamma-ray bursts are studied by astronomers.
The light coming from sun consists of all these radiation.
Their freequency varies.
Gamma rays are one such radiation.
You will study about all these in detail in higher classes.
Infact these are beyond the scope of discussion at this level.
Hope this helps.
Good luck.