Maybe a weird question, but what happen exactly during a ritual?
Depends on the demon involved, your own reasons for summoning…etc. every experience differs. Presence is felt; telepathy; invocation evocation etc
What happens in a ritual is very direct and personal.
You raise power, focus on your intent, and use the raised power to impose your intent on the universe and bend it to your will.
If you’re calling on other entities you’re basically sending out a request for them to manifest your will. If you’re using your own energy than you’re doing what Banjax said.
You create your world, that’s what magic means to me, by your willpower, maybe with the assistance of spiritual beings.