The mixer stage of a superheterodyne receiver is used to:

In a superheterodyne receiver, the primary function of the mixer stage is to convert the incoming radio frequency (RF) signal into a fixed intermediate frequency (IF). It achieves this by combining, or 'heterodyning', the incoming RF signal with a locally generated unmodulated signal from the local oscillator (LO). By converting various incoming frequencies to a single, fixed IF, the receiver can use highly tuned, fixed-frequency filters and amplifiers. This greatly improves the receiver's selectivity and gain compared to trying to tune filters across a wide band of frequencies. Other options describe different stages of the receiver. Removing image signals is the job of the RF front-end filters before the mixer, and producing an audio frequency for the speaker is the function of the detector or demodulator stage later in the circuit.