You'll get a long list of information about what's running and loaded on your system. To most of us, it will look like gibberish. But there are many places on the Web where you can get help deciphering your log file, and step-by-step instructions about how to get rid of any nasty malware lurking in your system.
Try Running an Automated Analysis
If you feel comfortable rooting around in the guts of your registry and are already familiar with many of the processes necessary to run your PC, you may want to try an automated analysis tool first, such as the one at HijackThis.de. Just paste the contents of your HijackThis log into the space provided, and click the Analyze button.
Automated Analysis Report
You'll get a report similar to the one above, with different items rated at different levels of safety. There will be some ambiguous items, however, and that's where you'll need to rely on your own knowledge, or seek further help.
Go to a Forum for Special Help
At Merijn.org, you'll find a list forums where you can post your HijackThis log file to get personal help with your infestation.
You'll want to post your log as a new thread in the forum.
Post Your HijackThis Log
Make sure you post your full HijackThis log to the forum; they'll need the complete details to help. It may also be helpful to state what you've already tried to do to clean your system, and how far that got you.
Get an Expert's Tailored Advice
An expert who has been vetted by forum administrators will give you step-by-step instructions about what to do next, and follow up to make sure the problem is solved.