If you want to access Cortana on an Echo speaker, just say “Alexa, open Cortana” to use the assistant to check your emails, schedule and to-do lists. To summon Alexa on a Windows 10 computer, it’s the other way around: say “Cortana, open Alexa” to play Jeopardy, add items to your shopping list, check your Amazon order status or to control your smart home devices.
Since this rollout is still just a preview, you won’t be able to access some of the assistants’ features on the other company’s devices. You won’t be able to ask Alexa to read an audiobook for you on a Windows 10 PC, for instance, and you can’t ask Cortana to play music for you on an Echo speaker. The companies promise that the experience will become better and more robust as they become available to more people over time.