Hi and welcome Dolce

My first bike ride on my road bike was very similar to what you laid out. It was 12 miles (~19 km) roundtrip and on a nice, generally flat road with a wide shoulder and fairly limited traffic. It was perfect for getting used to the bike geometry and everything!

Do you have any specifically designated bike paths? Bike paths typically seem to be flatter and they are often protected from traffic. That might be another good way to get used to the bike.