An analog signal can assume an infinite number of voltage level. Due to this is not possible to send it directly to a microprocessor (or to a DSP) to eleaborate it.
These devices (as all the digital devices) operate on digital numbers that can assume a finite number of voltage levels (1bit=2 levels, 2bits=4levels, 3bits=8 levels...).
So if you take an analog signal and convert it to digital, the two will be almost identical. "Almost" because reducing the number of levels you will loose something of the original analog signal, but choosing a correct number of bits to represent the signal, you will loose a negligible part of information.
So, assuming your analog signal is properly sampled (not only in terms of bits, but also as sampling frequency and antialias filtering), you will have an accurate digital copy of it, ready to be elaborated.