Please contact your hosting company to buy the domain names for your websites. For ideas about the domain names, try to think about some key words related to the domain name you want e.g. Article Marketing - try to think of a domain related to article marketing i.e. Top Article Marketing.com or Article Marketing 123.com
I do suggest you go for a .com domain name as these are the most popular and a worldwide domain however don't be afraid to try others as .com are becoming increasingly hard to find.
Do take a little time and write down a few ideas which you think are good names then run them through a domain name search facility to see if they are available.
Here is a link to check for domains look on the right of the page at the domain search facility http://www.freemonthlywebsites2.com/special/d9