HijackThis is an easy way to find out any errors in the system either with the registry or with the other things. What it does is, it scans the common areas of the computer, registry and hard disks and compares them with the default settings. If it comes across some dissimilarity then it saves it to the log file.
But analyzing this log file called HijackThis or HJT is not easy and require much of the background knowledge of the computers. Here are few sites/tool that can automatically analyze the HJT log file for you and will give you the recommendations based on the analysis.
Either copy paste the log file or upload it directly, the site will get you the analysis report easily and as correct as possible.
This is another simple online site to analyze the HJT log file, and the advantage being the color coding for the risks and the safe items.
HijackReader is a free application which reads HijackThis log files and tries to give advice on what to fix. It is a simple tool to help you get the analysis.
These sites or tool provided above would help you in getting the analysis report as correct as possible.