Visual Studio - Debugging SharePoint

In order to debug SharePoint within Visual Studio you need to attach visual studio debugger to the appropriate process.

You can attach the debugger to the process through:

The process you need to attach visual studio to depends on the type of solution you are developing.

Solution Type	Process
Web Part	w3wp.exe
Visual Web Part	w3wp.exe
Application Pages	w3wp.exe
Timer Jobs	owstimer.exe
Sandbox solution	spucworkerprocess.exe

SharePoint Timer Jobs
If you want to debug a SharePoint Timer Job ensure that the SharePoint Timer Service is running then attach the debugger to the owstimer,exe process within Visual Studio.
Within Central Administration navigate to:

Run the desired timer job and after a second or two the debugger should enter the break point within the timer job.