When is "i", "gli" and "le" used? First I thought that le and gli was used only when the noun began with a vowel because it seemed to be the pattern, but then le birre appears. Why?
"i" and "gli" is used for plural of masculine noun. "le" and "l + apostrophe" is for plural of feminine noun. And yes, birra (beer) is feminine in Italian. See previous comment for further info.