After downloading a Joomla Extension, you must first UNZIP the package.

Inside the package you will see the installable extension packs.

This can be a module, component or plugin.

To install the Joomla extension, you must go to the installer in your site's administration panel.

You can find the Joomla Installer in the admin area of your Joomla website, 
link : administrator/index.php?option=com_installer&view=install

You will receive a success message after successful installation.

Now you can start the installation of the extension.

If you installed a Plugin : 

Go to Plugins section and make a search for Extension
link: administrator/index.php?option=com_plugins

If you installed a Module: 

Go to Modules section and make a search for Extension
link: administrator/index.php?option=com_modules

If you installed a Component: 

Extension will appear at components dropdown list.

All Joomla Extensions developed by CodePlazza  are compatible with Joomla 4 and Joomla 3