Responsive Gallery Lightbox is a lightweight, responsive, mobile-friendly jQuery plugin for displaying an image/video gallery in a fullscreen lightbox …

Noted That:

To install correctly this responsive-gallery-lightbox.zip.
Fisrt Download the responsive-gallery-lightbox.zip to your computer
Extract/Open responsive-gallery-lightbox.zip to Your Computer.
Then, Find readme.txt file inside responsive-gallery-lightbox.zip and Open readme.txt.
Now, Read the Requirements of this plugin. Which Wordpress Version and PHP Version are required to run this Plugin in Your Wordpress Site.
Then, Follow the the Tips Below.

Start the Tips:

1. First Download "responsive-gallery-lightbox.zip" Plugin to your Local Computer. (Click Download)

2. Then, Login to your "yourdomain.com/wp-admin" Dashboard.

3. Then, Click on "Plugins" + "Add New" from left sidemenu of Dashboard.

4. Now, Click on "Upload Plugin" button.

5. Now, Browse "responsive-gallery-lightbox.zip" Downloaded plugin from your computer, Where you downloaded responsive-gallery-lightbox.zip According to Step – 1 Above then, click on "Install Now"

6. Now, Click on "Active Plugin"

7. Then, See left sidemenu. "Responsive Gallery Lightbox" folder is added on left sidemenu. Now, Click on "Responsive Gallery Lightbox" folder.

Noted that: If you do not see "Responsive Gallery Lightbox" folder on left sidemenu then, see at left sidemenu "Settings" or "Tools".

8. Now you configure yourself oR Watch video tutorial below about Responsive Gallery Lightbox Configurtions and Settings or How to work "Responsive Gallery Lightbox" in your WordPress site.

After Activated Plugin According to Step-6 then,

Go to "Plugins" + "Installed Plugin" from Wordpress Admin Panel Leftside Menu.
or Direct go to: https://yourdomain/wp-admin/plugins.php
Then, Find "Responsive Gallery Lightbox" Activated Plugin from Plugin List.
Then, Click on "Settings" from Plugin that is Responsive Gallery Lightbox
Now, Edit/Add/Config the setting and Click on "Save Changes" button,

Guide

Guide
Installing this plugin as regular wordpress plugin. After install, this plugin enable a custom post called Gallery Items. Add category & items on that custom post. After adding items, you are ready to use this plugin in your post, page, widget or anywhere you like. Go to page > Add New. On the editor, you will see a button called Gallery Shortcode by clicking button you see the shortcode like `[rsgallery category="Category_Name"]` Use category title, not category id or slag. Make sure spelling is ok. It is case sensitive.

Installing this plugin as regular wordpress plugin.

After install, this plugin enable a custom post called Gallery Items. Add category & items on that custom post.
After adding items, you are ready to use this plugin in your post, page, widget or anywhere you like.

Go to page > Add New. On the editor, you will see a button called Gallery Shortcode by clicking button you see the shortcode like [rsgallery category="Category_Name"]

Use category title, not category id or slag. Make sure spelling is ok. It is case sensitive.

lightbox, gallery, responsive, displaying, fullscreen, plugin, imagevideo, friendly, lightweight, mobile,

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Reffered: https://wordpress.org/