As a new user, you may wonder why manufacturers configure PCs with so many ports. To answer that question, let's ask another: why would you have two different types of shoes in your closet, say hiking shoes and bowling shoes?
The answer to both questions is that both types of shoes or ports have a specific purpose. You would not want to wear your bowling shoes to go hiking just as you would not want to connect a printer to a serial port. The shoes just wouldn't cut it on the hike, and the serial port is much too slow for fast efficient printing.
Each port, like each pair of shoes, has a specific function. Parallel ports are usually for fast data transfer, while serial ports are for slower data transfer. PS/2 ports are for keyboards and mice.