An IP address is a unique identifier. A protocol is a specification that describes how computers will talk to each other on a network. Data over the Internet is transferred in packets. Transmission Control Protocol or TCP makes sure the packets have arrived and the message is complete. Domain names, like IP addresses, are the method used to access a website.
People remember words much easier than numbers.
A website can be accessed either way. Either the IP address or Domain Name would work. Domain names are split into different categories depending on the function and affiliation of organizations. When you use the name of a domain, your computer looks up the corresponding number to address the packets, and the computer on the other end can look up the number to find out the name that they came from. The only valid characters for a domain name are letters, numbers and a hyphen.