Generally a dash is used here just as so called copula is used in English. So your guess is right, dash here is a some kind of punctuational copula, therefore can be translated as "is".
— это is indeed another form of such copula, there is a subtle difference between usage of these two forms. Roughly speaking, pure punctuational form is more universal, you can use it in a wider set of cases.
You can say, for example:
Вы — подлец!
But this phrase will sound definitely unnatural to native speaker:
Вы — это подлец.
So, with personal pronouns usage of
это is untypical.
As for me, it is very difficult to describe exact rules for choosing one these forms, but here is a rule of thumb that can give you a hint. If you can imagine the phrase used in some kind of dictionary as an article, for example:
- Париж — столица Франции.
- Слон — млекопитающее.
- Солнце — звезда.
then you can use
— это form.
Also, when you want to emphasise the second part of phrase, you can use
это. So, when you can imagine this very phrase used with some adjective, it looks like you cane use
- это form:
Пётр — [это] [ужасный] негодяй.