Alloys are made because they contain properties that the pure metal doesn't have, which makes them more useful in practical applications. Alloys can have special properties and can be harder than the original metal, more conductive to heat or electricity, or less prone to rust and corrosion.
Steel is a perfect example of an alloy. It is made by infusing iron with carbon. Iron in its original state is strong, but it's also naturally brittle and easily rusts. Steel is instead harder and resists rusting better than iron.
An example of an alloy with a special property is nitinol, which is made by mixing nickel and titanium. This mixture creates a material that serves as a memory alloy; if bent it can return to its original shape by either heating it or passing an electric current through it. This property is useful for spectacle frames as it allows for easy repair if bent.
Alloys are typically harder than the original metal because their structure contains atoms of different sizes, which makes the atomic layer harder to slide over itself.
Mixing metal with other elements creates alloys. These elements are melted to their liquid form and mixed together, or they are turned into powder that is mixed together and fused under high temperatures and pressures.