How to do debug the sharepoint application / libs / webparts in Visual Studio.
Step 1. Open the Sharepoint application(Source code) in Visual Studio
Step 2. Launch the Sharepoint in the browser.
Step 3. Go to Debug menu in Visual Studio.
Step 4. Click Attach to process.
Step 5. Select the W3P process in the Attach to Prcess window.
Step 6. Add break points into your sharepoint code.
Step 7. Navigate to your webpart / page,where the code is implemented.
Step 8. Now the breakpoint will hit in your code...