There are three parts: the input, the output, and the selector. With a mux, you have multiple inputs, and a selector chooses which one of those outputs to use, and pipes it to a single output.
10-Bit 2MSPS SAR Analog-to-Digital converter with 2-to-1 Mux in, UMC 55nm SP/RVT process. View A/D Converter IP, 10 bits, 2Msps, with 2-to-1 input MUX, UMC 55nm SP process full description to ...