No its not entered in the criteria its entered in the field row. You are creating new fields, the "criteria" for each sum is in the IIF and thus the Sum effectively becomes a count of that condition.
That's correct Dan, the way it works is that for each record in the table one of the 8 fields will reurn a 1 and the rest a 0 then the 1s are summed to give a count.
Don't worry about asking for clarification we all have to start somewhere and I've found that a lot of newcomers are puzzled by the use of Sum to get a count when there is a Count function.