Using custom JS plugins with WordPress?

Welcome (I’m new myself, too).

First and foremost, I highly recommend setting up a Child Theme for your Divi installation; that way any modifications you make won’t be overwritten when Elegant Themes do an update.

That said, the best way at this is to use WordPress’ native en queuing system. In your functions.php file, add the following:

function enqueue_particles() {
    wp_register_style('particles-styles', get_stylesheet_directory_uri() .'/particle.css', array());
    wp_enqueue_style('particles-styles');    
    wp_enqueue_script('particles-cdn', '//cdn.jsdelivr.net/particles.js/2.0.0/particles.min.js');
    wp_enqueue_script('particles-js', get_stylesheet_directory_uri() .'/particle.js', array('particles-cdn'));
}
add_action('wp_enqueue_scripts', 'enqueue_particles');

…then create 2 new files in your theme directory:

particle.css

canvas {
    display: block; 
}

#particles-js { 
    width: 100%; 
    height: 100vh; 
    background: -webkit-linear-gradient(top, #000000 1%, #0c0c24 100%);
    position: fixed;
    top: 0;
    left: 0;
    z-index: -50; 
}

…and particle.js

jQuery(document).ready(
    function() {
        particlesJS("particles-js", {
            "particles": {
                "number": {
                    "value": 160,
                    "density": {
                        "enable": true,
                        "value_area": 800
                    }
                },
                "color": {
                    "value": "#ffffff"
                },
                "shape": {
                    "type": "circle",
                    "stroke": {
                        "width": 0,
                        "color": "#000000"
                    },
                    "polygon": {
                        "nb_sides": 5
                    },
                    "image": {
                        "src": "img/github.svg",
                        "width": 100,
                        "height": 100
                    }
                },
                "opacity": {
                    "value": 1,
                    "random": true,
                    "anim": {
                        "enable": true,
                        "speed": 1,
                        "opacity_min": 0,
                        "sync": false
                    }
                },
                "size": {
                    "value": 3,
                    "random": true,
                    "anim": {
                        "enable": false,
                        "speed": 4,
                        "size_min": 0.3,
                        "sync": false
                    }
                },
                "line_linked": {
                    "enable": false,
                    "distance": 150,
                    "color": "#ffffff",
                    "opacity": 0.4,
                    "width": 1
                },
                "move": {
                    "enable": true,
                    "speed": 1,
                    "direction": "none",
                    "random": true,
                    "straight": false,
                    "out_mode": "out",
                    "bounce": false,
                    "attract": {
                        "enable": false,
                        "rotateX": 600,
                        "rotateY": 600
                    }
                }
            },
            "interactivity": {
                "detect_on": "window",
                "events": {
                    "onhover": {
                        "enable": false,
                        "mode": "grab"
                    },
                    "onclick": {
                        "enable": true,
                        "mode": "push"
                    },
                    "resize": true
                },
                "modes": {
                    "grab": {
                        "distance": 400,
                        "line_linked": {
                            "opacity": 1
                        }
                    },
                    "bubble": {
                        "distance": 250,
                        "size": 0,
                        "duration": 2,
                        "opacity": 0,
                        "speed": 3
                    },
                    "repulse": {
                        "distance": 400,
                        "duration": 0.4
                    },
                    "push": {
                        "particles_nb": 4
                    },
                    "remove": {
                        "particles_nb": 2
                    }
                }
            },
            "retina_detect": true
        });
    }
);

Good luck!