The Internic is a database of IP addresses and the Domain Names assigned to them. It's basically a phone directory for web sites. Domain Names all have an extension. There are others available with various requirements and costs involved. Tips for deciding on the right Domain Name.
Shorter names are easier to remember and spell.
A misspelled domain name is the same as the wrong name. Any name that is common is probably already taken, but you will not know until you research that domain name. Some companies have registered many names that they thought would be popular and then sell them for great deals of money. 3 letter names generally sell for several thousand dollars or more. When you register a Domain Name, you must pay whoever records your listing an annual fee to retain your Domain Name.