Once you signup for an API key at https://next.tagalys.com/signup and choose Magento 2.2 as your platform, you will find installation instructions within the dashboard.

Install the extension via Composer. Run the following commands on your server.

composer require tagalys/tagalys-search-magento2
php bin/magento module:enable Tagalys_Sync Tagalys_Analytics Tagalys_Search Tagalys_Mpages Tagalys_Mystore
php bin/magento setup:upgrade