There is no easy way to determine the gender of every noun, and you have to remember the gender with each word. But a number of patterns in suffixes and word endings are helpful: some tend to indicate masculine or feminine nouns (be careful with the exceptions).

Please have a look at this link:

http://french.about.com/od/grammar/a/genderpatterns.htm

It is a matter of context. If you buy "un pain" you will get a large baguette weighing @450g (at least in Paris, that may vary from region to region). Whereas "du pain" (some bread) is "a piece of bread", whichever the original form of the bread concerned.

You put "un pain" and you were right! the alternative could be "une miche de pain" but "un pain" is a good translation for "a loaf of bread".

It is a "noun of noun" case, where the second noun gives information (content, material, substance) about the first noun. In this case, the article is dropped:

• une feuille de papier = a sheet of paper (material)
• une miche de pain = a loaf of bread (substance)
• une bouteille de lait = a bottle of milk (content)

Note that "une miche du pain" = "a loaf of the bread", ie a specific bread, mentioned before.

You are right. And all the more if you consider that, at least in the Paris region, "un pain" is exactly like a baguette, but heavier (500g vs 250g). If you want to express the shape of "a loaf of bread" you will have to say "une miche de pain". Now, just for fun, in popular language "un pain" is a punch.

Because "beaucoup de pain" translates to "a lot of bread" (not "a loaf of bread").

In French, every noun has a gender, and you have to remember the gender of each noun. In general, nouns ending in "e" are feminine (but there are exceptions to this rule).

See: https://www.duolingo.com/comment/1101225

"un" is masculine, and refers to "pain" (masculine).

"une" is feminine, and refers to "miche" (feminine), which is made of bread (complement, masculine).