if so do i pay anything for using this service?
You would have to export your project to UNITY.
This link shows how to make a Unity project into an Android app.
You might be interested in this info
You are allowed to place ads into your ready games once they are transferred to Unity.
However - You will have to code them yourself, but there are many tutorials on the internet to help you out.
If I were to place ads right now, I’d choose Unity Ads as it is much simpler and there are so many tutorials for it.
Some ad providers do require you to pay them in order for them to also make a profit (because you know, business).