The actual domain name is the bit after the www. for a website address or after the @ symbol in an email.
The domain name is owned by a registrant who is the legal owner of the unique name.
Think of it as a sort of telephone number to access the beginning of a website or homepage.
If you type www.easykey.com in the address bar of your internet browser and press the enter key on your keyboard it will take you to the homepage of easykey.
It is common for this address to automatically change after you have typed in an address. This is because some website addresses are set to forward you on to another address or sub address. Try www.flash.com and watch what happens to the address in the address bar.
Many companies arrange that different addresses will take you to the same website. But instead of changing the domain the whole website is repeated using that domain. For example try going to www.easykey.com and navigate to different pages - you will see that they are all easykey.com/something.
Now try www.1to1help.com and navigate around that site. The whole site is repeated again but all using 1to1help.com/something
This is called aliasing - and the same technique can be applied for email addresses.
Using a domain for email
It is amazing how many people I meet that use their domain for their website but have an email using tesco.net, googlemail.com, aol.com, ntlworld.com etc. Just take a look at the van signage! If you own the domain name you really should use it for your email accounts. Theoretically you can have an unlimited number of email addresses e.g. email@example.com firstname.lastname@example.org email@example.com etc...