Hi Santhosh,
To do load test on webapplication, first you need to create a test case for your web application. One approach to create a test case for web based application is using selenium recording and importing the recorded file to Devtest test case.
Please go through video available in documentation to create test case.
Create and Export a Selenium Builder Recording - DevTest Solutions - 10.1 - CA Technologies Documentation
Once the test case is ready, you can create a staging doc based and choose the load pattern in "Base" tab. Go through below details for creating a staging document file.
Building Staging Documents - DevTest Solutions - 10.1 - CA Technologies Documentation
Run the test using staging document by selecting the created staging document (Make sure coordinator and simulator services are running). Refer below documentation for more details about staging the test case.
Stage a Test Case - DevTest Solutions - 10.1 - CA Technologies Documentation
Hope these details addressed your question.
Thanks
Srikanth