Dial-up IP connections use a modem to connect to a service provider which assigns you an IP address. Usually this IP address is temporary. After you hang up it will be used by someone else. Direct IP means you are directly hooked up to a network with a network card. In this case the IP address remains the same for the particular computer.
People find it easier to remember letters.
So we devised a domain hierarchy similar to a directory tree. IP addresses are converted into domain name addresses. Know what sort of organizations are included in each of these top level domains. Also treated as a top level domain is the two letter country code you will see in some addresses. For example, ca for Canada or au for Australia.