It depends on what you are looking to do. There are free forum software ( www.phpbb.com ) or paid ones ( www.vbulletin.com ), or you can find ones hosted by a company, I can't think of any websites that do that off the top of my head. It requires a lot of work to get started, a lot of patiance, and having loyal members help out is a good thing too.
Again that will depend. You can go with a hosting company that has the software all setup for you and the cost of the software can be included in a setup charge. There are companies that will host your forum for free. Or you can get soemthing like phpBB for free and pay a hosting company. Depending on the software you may or may not need a database. A good forum software will usually use a database since it will make it quicker, especially when the forum grows.
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