Depends, for a start at to get used to forums, use a free forum software such as PHPbb,
www.phpbb.com
Then you need some space to upload your files,
www.web-mania.com for a small site and pretty cheap. This includes a mySQL database for the forum.
Then you need a domain name,
www.namecheap.com
Probably around £30 per year for what you need. If you want decent forum software like mine, this can cost from £48 per year.