Similar to other types of .NET web development, Dynamics 365 uses the same technology stack under the hood. It is no surprise that debugging your custom code is similar to debugging a web application or service you have written.

After we enabled the breakpoint in the first step, we attached the Visual Studio debugger to the correct process that will be running your code.

Once your plugin is executed, the Visual Studio debugger will catch the event and break at the line that you have highlighted in step 1. You can then debug the code as you would debug any .NET application by stepping into the relevant sections, monitoring your variables, and following the call stack.

For further details, check out the following MSDN article: https://msdn.microsoft.com/en-us/library/gg328574.aspx.