Hi, it is simple. But I jsu quickly tell everyone to create a child theme first. It is easy, read it here: https://codex.www.ads-software.com/Child_Themes
Then copy the style.css and the header.php into the child theme.
Then edit the HEADER php , even if you don’t do the child them, just edit the HEADER.php in your theme editor.
Depending on the slideshow you use, I use Revolution slider, but you can use Meta slider which is free on WordPress. Once you activated the slider and created a slide, paste the slider code (Your code will be SIMILAR depending on your slider!! like this: ?php putRevSlider(“home1”) ?, into header.php like this example:
</head>
<body <?php body_class(); ?>>
<div id="page" class="hfeed site">
<header id="masthead" class="site-header" role="banner">
<a class="home-link" href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home">
<h1 class="site-title"><?php bloginfo( 'name' ); ?></h1>
<h2 class="site-description"><?php bloginfo( 'description' ); ?></h2>
</a>
<?php putRevSlider("home1") ?>
<div id="navbar" class="navbar">
<nav id="site-navigation" class="navigation main-navigation" role="navigation">
If you want your NAV bar on top of the slider, paste the slider code below the NAV bar code…
View the live example here: https://hartdesign.info/shop33/
Good luck, Groggo