Learn Dutch: Hé, dat is mijn fiets! - Hey, that is my bicycle!

The accent shows that the 'e' should be pronounced as a long vowel, sounding similar to the English word "hay". If the accent wasn't there, a single 'e' at the end of a short Dutch word is usually pronounced as a short "uh" sound (like in de).

Why do we use dat (that) if fiets is a de word? Shouldn't we use die?

When you are introducing or pointing something out by saying "that is" or "this is", Dutch always uses the fixed phrases dat is or dit is. It doesn't matter if the noun that follows is a de word or a het word. You would only use die if you were attaching it directly to the noun, like in die fiets (that bicycle).

Will I always hear Dutch speakers pronounce mijn exactly as it is spelled?

Not always! While mijn is the official spelling, in everyday relaxed speech, Dutch people very often shorten it to m'n, which sounds a bit like the English word "mun".