wam is your weighted average mark. for each course you finish you will get a mark out of 100. your wam is your average mark. so if you did 4 courses and got 60, 70, 70, and 80 your wam would be the average of those 4 which is 70.
wam needed for honours varies but it is usually set at a credit or a wam of 65. however if all of the top students decide to do honours then it is possible that people with a credit wam could still not get into honours. so there the only way to be guaranteed an honours year is to be one of the best students (like if there are 10 honours spots, be one of the best 10 students, if there are 90, get into the top 90)