Head Image Slider- HELP! I'm a novice WP user

Hi, I am new to WP and dreamweaver. I am trying to insert the header image slider plugin to the current website I am creating for my parent’s busienss.

A couple of things;
1. I made my theme from scratch from dreamweaver. I have a index.php and style.css
2. As you can see on my website, the slider is not showing up. I added this code in my index.php
<?php if( is_home() ) boom_header_image();?>
3. I don’t understand why you would need a header.php – i would appreciate if someone can explain it to me briefly.

Anyways please help me! You’re help will be greatly appreciated.