If you want to add a WordPress file upload to your form so that when you select a photo or video, its URL will be added to your input field, you can use this code.

• This HTML code must be used in the form

<label for="upload_file">
    <input id="upload_file" type="text" size="36" name="fileLink" value="" /> 
    <input id="upload_file_button" class="button" type="button" value="Upload File" />
    <br />Enter a URL or upload an File
</label>

• This PHP code must be used in the theme function.php or plugin php file.

<?php
add_action( 'admin_enqueue_scripts', 'my_admin_scripts' );

function my_admin_scripts() {
    if ( isset( $_GET['page'] ) && $_GET['page'] == 'my_plugin_page' ) {
        wp_enqueue_media();
        wp_register_script( 'my-admin-js', WP_PLUGIN_URL.'/my-plugin/my-admin.js', array( 'jquery' ) );
        wp_enqueue_script( 'my-admin-js' );
    }
}
?>

• This jQuery code must be used in the JS file.

jQuery(document).ready(function($){
    var customUploader;

    $('#upload_file_button').click(function(e) {

        e.preventDefault();

        //If the uploader object has already been created, reopen the dialog
        if (customUploader) {
            customUploader.open();
            return;
        }

        //Extend the wp.media object
        customUploader = wp.media.frames.file_frame = wp.media({
            title: 'Choose File',
            button: {
                text: 'Choose File'
            },
            multiple: true
        });

        //When a file is selected, grab the URL and set it as the text field's value
        customUploader.on('select', function() {
            console.log(customUploader.state().get('selection').toJSON());
            attachment = customUploader.state().get('selection').first().toJSON();
            $( '#upload_file' ).val( attachment.url );
        });

        //Open the uploader dialog
        customUploader.open();

    });
});