Generally speaking they are interchangeable, unless your intent is to emphasize the word "I". It's a little hard to explain but if what you really meant to say is "I AM a man," almost as though you were asserting it after being challenged, then you would want to use Io first. Otherwise either way is fine.
No. "I" in English is not removed at any time. We removed "you" more often....it's called "You Understood" in English grammar. If you ever said to someone "Eat the banana" meaning (I eat the banana) it would actually mean "You eat the banana"..........and it would be taken as a command and could come across as being somewhat rude. It's something that you would say to a child or to someone else that you feel comfortable giving instructions to. You would never speak like that to your boss or someone else in a 'respected' position. I hope that makes sense. You can take a look at this link. http://www.english-grammar-revolution.com/imperative-sentence.html (I could have also typed "Take a look at this link" and it would have been an informal request.)
"Un" is the masculine indefinite article......... equivalent to the English words "a" or "an." English does not have masculine and feminine designations for nouns, so we just is "he is a man" or "that is an apple." "Una" is the feminine indefinite article....used for feminine nouns such as "mela," "ragazza," and "bottiglia." VERY often, it sounds like she (the Duolingo speaker) is saying "una" when she is actually saying "un".....it can be very frustrating at times, but I've found that the more I use it the more my ear is 'tuned' to her "un" vs "una." Happy Learning! :-)
Yes. In all, there are an impressive seven ways to say "the" and four ways to say "an".
Use il for most masculine nouns, but use lo for masculine nouns starting with s+consonant, gn, pn, ps, x, y, z or a vowel.
Before vowels, lo contracs to l'.
Use la for most feminine nouns, but it too contracts to l' before vowels.
These all also have plural forms.
il piatto → i piatti
lo zaino → gli zaini
l'uomo → gli uomini
la vita → le vite
l'era → le ere
Use un where you would use il or (masc.) l', and use uno where you'd use lo.
Use una where you would use la and un' where you'd use fem. l'.
Use l' whenever a singular noun starts with a vowel or silent letter. It turns into gli or le in the plural, depending on whether the word is masculine or feminine.
You can usually tell a word's gender by what letter it ends in: masculine words usually end in -o, while feminine words usually end in -a.
Use un' whenever a feminine word starts with a vowel. You wouldn't use it with masculine words, because un' is just a contraction of una.
It would seem like whenever a word starts with a vowel sound, use un', but that only happens with feminine words.
Think of it like un' being a contraction of una. Since un is already a pretty short word, it doesn't need to be contracted any further.
That "un' uomo" contains a grammar mistake and a spelling error. Un' is the elision of una, a feminine article that cannot be used with a masculine name such as uomo; and in Italian spelling the elision joins two words, so there shouldn't be a space after the apostrophe (much like "shouldn't" or "it's").