Welcome to chapter five! I have deliberately left the discussion of articulation and staccato to after your first notes because I do not want to have the idea that a change of note equals a change in the air flow. I have seen too many students not grasp the idea of articulation and simply 'huff' the change of note. The association of change of note with change of air is a really hard association to break, and even I have to regularly refresh my thinking with long tone exercises. Yes, it takes a bit more time for you to play Hot Cross Buns, but it is worth it in the long run.
So, what is articulation? Articulation, or tonguing, is the action of the tongue hitting the reed, briefly stopping it from vibrating. The sensation of tongue touching (well, hitting is a little too strong), can be felt if one says 'da', where the tongue touches the back of the upper front teeth. I use 'da' rather than 'ta' as it is a little softer. I don't use 'du' because that changes the position of the mouth, and we don't want to do that. There should be absolutely no change in the embouchure or air when one is articulating.
Here is a YouTube clip I made in response to a query on how to form the embouchure for staccato. As you see, there is no change in the embouchure at all between the staccato and legato.
Ideally, you want to get the same tone for your articulation that you get for your legato. How you achieve this is to start playing a long note, then touch the tongue to the reed, and at a very slow speed, getting slightly faster, articulate. Try this on the lower register to start, then the throat tones, and gradually moving up to the upper registers. Note, that while articulating in the lower registers is relatively easy, once you hit the register key you may notice a 'thuh' undertone in the notes. You need to work very hard on this. Play lots of long tones on those notes, listening to the sound, then gradually bring the tongue into play. Try to get rid of the 'thuh' undertone. With regards to the altissimo register, the same applies, though in this case you don't want to overblow to the higher notes, ie, overblowing to A when you want to play E.
