Think of it like a line of people waiting for a bus where the stronger person (more reactive metal) can push the weaker person (less reactive metal) out of their spot in the queue.

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This follows the electrochemical series where metals are arranged based on their standard reduction potential. A metal with a more negative reduction potential can lose electrons more easily (oxidation) and displace a metal with a higher (less negative) reduction potential from its salt solution. The reaction can be generalized as $M_1 + M_2^{n+} \text{Salt} \rightarrow M_1^{n+} \text{Salt} + M_2$ if $M_1$ is higher in the reactivity series than $M_2$.

Always remember that the metal being displaced must be in an ionic form ($M^{n+}$) in solution for the reaction to occur; displacement cannot happen between two solid metals.