sure =),
Yes $('.hideable') selects all elements with class="hideable" and puts them in a sort of array.
when you say $(this) your basically talking to an array object BUT you want to address the elements inside correct?
So you have to pass in "e" short for event(you could give it any name its a variable).
the "e" (event) is an object with tons and tons of stuff in it. One of those it "target" and it is referring to the element you clicked.
so in English it is the event target. That's your selector to the clicked element!
Hope this answered your question!