Hi!
The normal stuff is like what you see in the stock repeater when you drag it onto the page: essentially setting the values of the items in your row.
Set text of (rectangle) to [[Item.Column0]]
Also, anything in brackets is an expression, so Axure uses the result of the expression rather than treating like normal text. For instance, Set text of widget cost to $[[ 1 + 1]].00 would set the text to $2.00, since Axure treats the part inside of the double brackets as something it needs to evaluate.
Target.text gets the text of the thing that your command is acting upon, so…
Set text of widget boyCount to [[Target.text + 1]]
…gets the existing text of boyCount, adds one to it, and then set boyCount to the result. Keep in mind that Item Loaded runs once for each row in your repeater, so if your repeater has 30 rows, it will run 30 times. Because of the third IF statement above, each time Item Loaded runs into a row whose childType is Boy, it increments boyCount.
Here is some recommended reading that might clear things up.
Using local variables, This, and Target
Understanding Axure’s repeater widget
Let me know if you stuck!