Modern bicycle pedals are made out of many different materials. The composition of the pedal you choose should match your need. If you are a casual rider, a common metal and plastic platform pedal would be fine. If you plan on racing or doing fast club rides and centuries, a clipless pedal in durable lightweight materials might be what you need.
Pedals were first attached to bicycles in the 1860s. In the 1980s the first clipless varieties were invented, which attach to the shoe of the rider.
Less expensive bikes have pedals that are usually made of common metals like steel and aluminum and/or plastics. Expensive racing bikes usually have clipless pedals constructed of titanium, high-grade aluminum and/or carbon fiber.
The more expensive materials like carbon fiber and titanium are lighter and stronger than their cheaper counterparts. These materials are used for higher-end bike pedals.
The casual rider does not need to invest in a higher-end pedal made of expensive materials. There are many clipless and platform pedals made of cheaper materials that will work fine.
If you are planning on racing, a pedal made of carbon fiber, titanium or other premium materials might be worth the expense for you.