Because there's every chance you need a refresher course, particularly in this age of complete tools still telling me in 2012 that volcanoes are to blame...
These short critical-thinking videos were designed by the Australian Gov't as teaching aids for teachers with year 8-10 students (13-15yr olds). The videos could be viewed as part of virtually any curriculum.
Video 1,2,3 are very basic with singular examples. The remainder (of 6 videos) elaborate and conclude in very clean summaries.
All six linked here.
Or start with number 1 here. (very simple, I promise it gets better from three onward)
