I would like to watch DC series and wanted to know if I might have to change there so that I understand it better.
I only have Netflix…
Yes, some have
I know that Supergirl and Arrow play together and in the future also The Flash = Arrowverse
My recommendation: It doesn't matter which series you start with, everyone is cool. I started with Green Arrow and then Supergirl. In some episodes they even meet (usually one episode per season)
The Arrow-Verse series are all bad.
Look at Titans, the series is not part of it and is better than everyone.