In this case, this is what you should do:
Download the folder with the plugin (tilda) to the folder /wp-content/plugins
Go to the website dashboard
Go to the plugins page (Plugins/Installed)
Find the plugin Tilda Publishing API and click "Activate"
Get the public and private keys. To do this, open the tab API in your account and click "Generate Keys". https://tilda.cc/identity/apikeys/
Go to Settings > Tilda Publishing
Insert the private and public keys generated by Tilda. Save.