You need 3 things to have a working forum
1) A domain name
2) A hosting package
3) Actual forum software
Many hosting packages will throw in a free domain name- this will make your life easier although in the long run it is better you have your domain separate from your host. Popular places to register domain names are GoDaddy and Network Solutions.
For a decent vBulletin host you will be looking at $10 to $25 a month although there may be cheaper options you get what you pay for. Please don't use GoDaddy for hosting vBulletin, they are horrible hosts. You can find out about quality hosts on
vBulletin.com Hosting Talk.
Those are prices for basic shared hosting- ideal for a small/new site. If your site actually takes off and generates hundreds or thousands of visits per day you will need to upgrade hosting but you can cross that bridge when/if you come to it.
Of course I think setting up and installing vBulletin is easy but I'm a computer person. Most people who buy it are able to install it themselves though. Here are the instructions if you want to look them over first:
https://www.vbulletin.com/docs/html/install