Some protocols are simpler than others, some are more reliable, and some are faster. They can be implemented either in software or in hardware. From a users view, you only need to know that your computer or device must support the right protocols if you want to communicate with other computers. Each gateway computer on the network checks this address to see where to forward the message. Regardless of how they are routed, packets are reassembled correctly at their destination.
Clients are PCs or workstations on which users run applications.