If your new to running websites / forums and looking to promote your website online, I would suggest you try write up a well worded advertisement, stating what your website is about, key points about what is on offer and why should users visit / signup on your website.
You could start with posting that ad in forums similar to your own website, if people respond asking for more information, be polite and respond to their questions.
Use social media, setup Facebook, Twitter etc accounts up and post regular updates. Follow people that you think maybe interested in your website, share their posts / tweets! In turn they may reciprocate the gesture and share your posts.
Post comments in blogs with your thoughts with a link within your post, don`t spam as your less likely to have those comments accepted on blogs.
Make sure your website is optimized for the search engines, meaning make sure page titles/ meta titles match the page content on the page.
Add your website to directories similar to your website, earning yourself back links, the more good quality links your website has the better the chance of it ranking on the search engines.
The best advice I can give you is, keep your website upto date, add new pages content on a weekly / monthly basis as to keep the visitors you gained coming back time and time again.
Once your website starts to grow, people will talk about your website online and you will most likely gain many more visitors.