Is there meant to be 'ettiquette' around Halloween and trick-or-treating?

My 9 y/o wants me to say yes to taking her to one of her school friends places for a big halloween party with trick-or-treating, etc. and I've never done anything like it before. Halloween is a 'foreign concept' for us Aussies. I don't understand what it's about or what the big deal of it is. Other than marketing to children.