The person on the roundabout has priority over the person entering. That's what makes roundabouts work, the other way around, you would keep getting gridlock.
As you approach a roundabout, you slow down so you can merge into the traffic already on the roundabout. if it works, you don't have to stop.
Never right on red. Unless there is a special green arrow traffic light or sign.
If you are planning to drive in any country you have never driven in before, you need to research the road rules and the road signs first. It is your duty to know the law, ignorance of the law is no defence.
One place to look is here: https://www.theaa.com/european-breakdown-cover/driving-in-europe/country-by-country
This is the British Automobile Association. It is written for British drivers, so it explains the differences between each country and British rules, for example it doesn't mention you can't turn right on red, as you can't do that in the UK or any other European country. But it is worth reading.