RF amplifiers (also known as boots, burners, kickers, help etc) boost the output power of your radio - so increasing the transmit range.
All amps have a maximum and minimum power which they need to drive them. If used on a radio with too high output it is likely the amp will be damaged.
You must ensure that your antenna is correctly tuned before fitting an amplifier. If the swr is high it will damage the amplifier, blowing the output transistor(s)