Apache JMeter is a 100% pure Java desktop application designed to load test client/server software. It may be used to test performance both on static and dynamic resources such as static files, Java Servlets, CGI scripts, Java objects, databases, FTP servers, and more. JMeter can be used to simulate a heavy load on a server, network or object to test its strength or to analyze overall performance under different load types.

Version

Go for apache Jmeter 2.3.4 which supports Badboy Scripts as we have to record web application scripts using Badboy tool and import the scripts from Badboy to Jmeter.
Overview of the Jmeter Components:

Thread Group

Thread group elements are the beginning points of any test plan.
All controllers and samplers must be under a thread group.
Other elements, e.g. Listeners, may be placed directly under the test plan, in which case they will apply to all the thread groups.
As the name implies, the thread group element controls the number of threads JMeter will use to execute your test. The controls for a thread group allow you to:
• Set the number of threads
• Set the ramp-up period
• Set the number of times to execute the test

Ramp-up period

The ramp-up period tells JMeter how long to take to “ramp-up” to the full number of threads chosen.
If 10 threads are used, and the ramp-up period is 100 seconds, then JMeter will take 100 seconds to get all 10 threads up and running. Each thread will start 10 (100/10) seconds after the previous thread was begun. If there are 30 threads and a ramp-up period of 120 seconds, then each successive thread will be delayed by 4 seconds.

How to define Ramp-Up Period???

Ramp-up needs to be long enough to avoid too large a work-load at the start of a test, and short enough that the last threads start running before the first ones finish (unless one wants that to happen).
Start with Ramp-up = number of threads and adjust up or down as needed.
By default, the thread group is configured to loop once through its elementsSamplers:
Samplers perform the actual work of JMeter. Each sampler (except Test Action) generates one or more sample results. The sample results have various attributes (success/fail, elapsed time, data size etc) and can be viewed in the various listeners.