What is the purpose of carrier signal in modulation?

Carrier signal is of high frequencies, it gives strength to the original signal because original signal cannot travel long distances so it needs to be strengthen a bit for transmitting.

The carrier signal is a high frequency signal, called an RF. Radio Frequency signal, it is to high for the human or animal ear to detect it, so its outside the audible spectrum and can easily be transmitted over the air to receivers that is tuned to receive that frequency and detect any modulation on that signal.