"è" means "is". In Italian you're allowed to skip the "she". So a literal English translation would be "is a sweet girl", but that's ungrammatical so you have to supply the "she". Theoretically it could also be "he is a sweet girl" or "it is a sweet girl", but obviously "she" is the most likely choice!
It is confusing to me and I'm a native Chinese speaker. Having said that, I guess the whole Italian language confuses me (especially the gender thing). This is the most fascinating side of learning languages... Getting to know how people from different cultures express themselves differently
More than you want to know.
Nice list of adjectives that USUALLY go in front of the noun.
And all of the exceptions and other rules. http://www.italyheritage.com/learn-italian/course/grammar/adjectives.htm
Because, like a lot of romance languages such as Italian and French apart from some exceptions the adjective comes after the noun. When we translate it into English we shift the adjective to before the noun because that's how it works in English, but it doesn't work that way in most cases in Italian (I know French has some exceptions, I'm less sure about Italian ones)
In general in Italian, the pronouns are not used. I have found DL confusing because in the early lessons pronouns have always been used. As you progress, you'll get used to it. I regularly type answers in Italian without the pronouns and they are accepted. Some of the multiple choice questions at this level omit the pronouns.
Interestingly (to me anyway) is that in learning Welsh (at night school and here) pronouns are always used, but I've got to the stage of reading "proper" books (as opposed to learners' books) and I find the pronouns are often dropped there too! It's like reading Italian....