To put it simply, a windows registry is basically just a huge database of records. This database stores every single hardware & software configuration, settings on your computer. It is organized in a hierarchical model and can contain hundreds of thousands of entries.
You usually will not need to fix or clean the windows registry when your computer is new. However, after a period of time depending on the usage of your computer, you may need to perform some registry cleaning to remove unnecessary and obsolete entries.
The windows registry grows in size primarily because of new hardware and software programs being installed on the computer. Even a simple plugin for your internet explorer such as flash or quicktime is recorded in the windows registry.
There are some software programs and drivers that do not remove the entries from the windows registry when it is being uninstalled. As a result, they become obsolete and taking up memory space on your computer.
The windows registry contains thousands of entries which can be difficult to understand and sometimes unreadable and I would recommend not to clean the windows registry manually unless you know...