The Unity Profiler looks at the hardware in use and how it is being used. At the same time, it is using the application that is running and breaking it down into method calls. It breaks each method call down to a percentage of use, as well as memory allocation and other elements. In the following screenshot, you can see the skeeball game running and how the methods are being broken down to use percentages:
This can be really useful for finding a method that is taking up way more process than it should be.