A good place to start when creating an administrator dashboard is storing values in a database and then building an administrator dashboard around those stored values so you can populate your site dynamically.
For the sake of simplicity let's say you wanted the ability to change the color of your navbar through the admin dashoard. You could accomplish this by storing the current color of the nav in a database and then echoing out the current color you wanted by making a call in you php file with SQL.
For example inside of the database you have the row nav_color
set to #000000
in effect when the file executes your navbar would be that hex color in this case black. You could effectively update that color code in the database to #ffffff
changing the navbar color to white.
File showing Navbar:
<?php
// Create connection
$conn = new mysqli('localhost', 'username', 'pass', 'database');
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT * FROM homepage_colors";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
// output data of each row
while($row = $result->fetch_assoc()) {
$nav_color = $row['nav_color'];
}
}
$conn->close();
?>
<!DOCTYPE html>
<html>
<body>
<nav style="color: <?php echo $nav_color; ?>"></nav>
</body>
</html>
As you can see this can be a lot of work, and can become a lot of backend development. Making requests to the database to pull information to populate your site. This is also a very very simple example, and doesn't take into account all of the security you need to build in to prevent different types of attacks on your site such as SQL Injection
I would suggest if you want to learn about creating an administrator dashboard for your site focus on learning about backend development, databases, SQL Queries, and good security practices.