Discord: paste a webhook URL (Server Settings, then Integrations, then Webhooks) and hit test.
Email: add one or more addresses, then choose which events email you (restocks, price drops, new products, stock-outs).
Telegram: connect a chat to receive alerts there.
You can also choose which priorities you receive: Critical (restocks, big price drops), Important (new products, minor drops) and Info (stock and content changes).
To send different products to different places, see keyword routing.