First you need to create one or more Web Performance Tests. It's in this test that you define which urls should be hit in the test and how it should happen (GET, POST, loop, conditions, headers, ...). You can add a new Web Performance Test by simply right clicking your project, Add, New Web Performance Test.
After you created your test, simply add them in a scenario of your load test:
This should get you started. To get the most out of load testing I suggest you do some more reading about the topic because there's a lot more to it.