The script just adds a column called OrderCounter with the single value of 1. The reason for this is to give a different way to count the number of orders, so instead of count(OrderId) use sum(OrderCounter). Some believe there is a performance improvement in doing it that way. I'm not so sure there is but it's easy to try it out.
If your second question asks if you need to do something like this when loading your tables then no is the answer.
There are many ways to add your two tables to QV. The simplest might be concatenation. In the script below I've changed the name of the two date fields to Date and added a new field to each called Transaction Type.
LOAD * , 'Expenditure' as [Transaction Type] INLINE [