Get your website a domain name. It is the address that your website can be accessed from like yahoo.com or Wikipedia.org etc.
You will have to buy the rights or outsource it to the hosting website. They will host your website online for a particular time period and cost you some dollars in response for their services. They will provide you an online space and software required to run everything on your website. Everyone across the globe can access your website through browsing software when the hosting company brings it live.
You need to install the software that will be supported by your forum. Use Fantastico for this purpose. They will do this service for you without an added effort. Currently most web hosts have phpBB, vBulletin and SMF forum softwares available in their Fantastico.
You have to create a forum administrator who will moderate everything on the forum. He will have a special username and password and added rights to edit posts; deletion and insertion of new threads can also be the added rights of administrator who will make sure that everything discussed is well within the limits set by your agreement and no one breaches the limits without any notice or dismissal.
The header of each page is to be designed in this step. You will have to make sure that your website or organisation’s name is placed at the top of the forum along with some informative description telling the domain of the discussions and characters that are to be used and not used etc.
Define categories and bring your forum live on the internet to accomplish your goal.