In the communication principle, "digital modulation is to shift the frequency spectrum of digital baseband signal to high frequency", which means baseband signal? How to complete the moving frequency?

In the communication principle, "digital modulation is to shift the frequency spectrum of digital baseband signal to high frequency", which means baseband signal? How to complete the moving frequency? adoption in layman's terms, baseband signal is the signal you need to transmit. The purpose of spectrum shifting is to move the baseband signal with low frequency to high frequency by certain means. For example, the center frequency of your baseband signal is 1Hz, the bandwidth is 5Hz, the signal frequency is very low, and the transmission effect is very poor. Then we use a high-frequency carrier, such as a 1MHz sine wave, to move the baseband signal near the high-frequency carrier. It can be understood that at this time, the central frequency of the baseband signal has reached 1MHz, and the bandwidth is still 5Hz. Formula is hard to say. Different modulation methods have different corresponding calculation formulas. But you should know the formula of modulation theorem. F (t) cos (WC * t)-1/2 [f (w+WC)+f (w-WC)], the formula probably explains the meaning of spectrum shift.