The use of contexts is necessary when you want to create different and totally isolated routing scenarios for voice calls.
In order to better understand how it works, just think about the sets concept, by imagining some isolated environments.
To create a new context go on Voice ➡️ Contexts and click on + button:
In each of these isolated environments you may involve one or more routes pointing to a destination, which can be for example a dial or a queue.
Consequently Notice that a route inside the Context SUPPORT will be not able to be involved by the Context SALES etc.
So you have to create a context for each queue and an internal route for each context:
Then you may also add a queue in the actions of the internal route already assigned to a certain context: