You can install Redactor Tweaks via the plugin store, or through Composer.
To install Redactor Tweaks, navigate to the Plugin Store section of your Craft control panel, search for
Redactor Tweaks, and click the Try button.
You can also add the package to your project using Composer and the command line.
Open your terminal and go to your Craft project:
Then tell Composer to require the plugin, and Craft to install it:
composer require verbb/redactor-tweaks && php craft plugin/install redactor-tweaks