"a" is like "the", "the shirt" "a camisa". "Há", is like having something. "There is eggs here" "Há ovos aqui". So when you listen, you need to try to understand what is the situation, you will need to translate the phrase, only then you will know.
Can I say "tem uma grande diferença"? If not, what is the difference between tem and há?
Thank you, that clears it up for me, since I was wondering the same thing.
Do they both sound the same? I translated it as "the one big difference", and it was marked wrong. For example: The one big difference between us is that you are tall and I am short.
Yes. They sound the same. I think you should write: "The only big...", in portuguese: "A única grande...".
Why is "grande" not after "diferença". Wouldn't "grande" be an adjective, making it come after?
Many adjectives in Portuguese can go either before or after the nouns they modify. Note that, some of them generate different meanings in accord with its position.