my (very limited) understanding is that the main things you need to know about entropy is just how the relationship between change and entropy and change in enthalpy affects spontaneity of reactions (Gibbs free energy). I don't think the course really goes too deep into entropy (i don't think we have to be able to calculate it???) so its probably not a big worry.
Entropy of mixing specifically will always be positive (more disorderly). If you picture two different gasses, contained separately which are then mixed, they move from being fairly ordered (separated and contained) to be less ordered (molecules of different gasses 'sprinkled' around and not in any particular arrangement). I don't believe you would really need to know any more than that, and i also doubt that they would ask much about entropy aside from giving you a reaction and asking something related to gibbs free energy and spontaneity.