Now that we have no chip system, can we post unoriginal material now?
Like this?

How do I keep my forum spam free?

Spammers spam anything that isn't nailed down completely. So, how to keep a forum spam free?
I'm clueless, so please keep it simple...
If your spam is overrun by spam, and you don't have premoderation capabilities (ie, when the messages won't appear on the forum before you approve them), then you need to delete your forum. It's possible your forum contains the capability of moderation, but you'll have to check in the admin panel and switch it on.
If one or two spammers have found your forum, but they've only made one spam run each, there's a chance you could salvage the forum. BUT, you'll need to remove it from the search engines right away, to avoid attracting another spammer that won't go away.
You do that by placing a robots.txt file in the root of your site. That means, the same directory as your first index. file. NOT where the forum resides. In that file, you need to put the following text:
User-agent: *
Disallow: /forumdirectory/
And remember to put the name of your forumdirectory in here, not copy the text word by word.
If you need to start over, and have a very small site, and are truly clueless, you may not be able to use any of the really big and complicated forums. They ARE better because people need to register before they can post, and some have premoderation that can be turned on and off for subforums.
So, if you need to start over with what many would term insecure software (like Matt's wwwboard and its clones), you should pick a new directory, disallow that directory in robots.txt before you start, install your forum and pray... Spammers will generally not be interested in your forum unless they find it on Google, but if your forum gets busy, it might attract trolls, which could be quite annoying.
I'm fairly experienced with websites. I just want advice on keeping my forum free of spam...
If you have a big website (ie, plenty of space), you're probably using a forum powered by MySQL. vBulletin, Invision Power Board, phpBB or Simple Machines.
That kind of forum usually has less of a problem with spam, because users need to be registered. But there are spambots that can manage registering accounts. If you install captcha's for registering accounts, you should have less of a problem. That's built into some forum software. Just choose that feature in the admin panel.
If you have a large problem with spam (say if you allow unregistered users to post), you may need premoderation. That's currently not possible with phpBB, but that functionality is coming. Most of the other forums already have that feature.
If you have a really bad problem - say humans registering accounts and spamming as though they're a troll - moderate new users. Approve them for unmoderated posting only after they've posted a number of posts.
I should also mention something about search engine spiders: Some forum software can lead Googlebot and msnbot and possibly other bots to get lost inside your forum, maybe even taking down your server, because they get lost in all the session ID's. That's a problem with some versions of Invision Power Board, and may be a problem with other software using session ID's. There are mods out there, so investigate that before you let search engines loose on your forum.

It's a crazy world out there.