Info here: How to use Gmer? - Anti-Virus and Anti-Malware Software
If you're unsure how to use a particular Anti-rootkit (ARK) tool or interpret the log it generates, then you probably should not be using it. Some ARK tools like GMER are intended for advanced users or to be used under the guidance of an expert who can interpret the log results and investigate it for malicious entries before taking any removal action. Even with advanced training, trying to interpret GMER results can be confusing at best as there could be many legitimate entries in its log.