You can download xampp from Apache-friends. In there select your operating system such as windows / Linux etc.. Then in the download section click on xampp. Then you will see the link called "installer" click on it. and your download will start and it.
Download and install the software to your computer. If the application control start automatically it is fine. If not you can go to the folder where the xampp is downloaded and then check for xampp control click on it and open it.
Then what you have to do is starting Apache to access to our localhost. So you click on the start button right in front of Apache. And that you will see it starts running.