You don't need a website to start a forum. But starting a forum is really not easy, unless you already have a community with a lot of people ready to post in your forum.
If it is totally new, it will be very hard to get people to know about it, and even more to have them post and come back on a regular basis, because no one wants to post and bring alive a forum that is not alive yet.
So to get people to post and come back to your forum, it has to be filled with a lot of conversations already. The only way to achieve this might be either :
- Create multiple accounts yourself and make the conversations (which will take ages)
- Use a forum autoposter, that will create accounts, post and answer a bunch of threads scrapped from other forums or from yahoo answer (yahoo answer looks like a great source of content for the kind of forum you want to create).
Once your forum is filled with a lot of threads, conversations, and seem to have a lot of (fictive) active members, threads will be likely to be indexed in search engines, and real people who will eventually stumble across your forum will be more likely to sign up and start posting for real.
If you can manage to achieve this, your forum will make a killing, but you can't do this overnight, it will take a lot of time and effort, and you should never give up
