I just wanted to add, for completeness, to the note in lesson 7 about the double 't' changing to 'tsu': It actually changes to a 1/2 sized tsu: っ vs つ
This small tsu represents a "glottal stop" which is like the sound in the middle of "uh-oh" -- that little pause thingy. So for まって (matte = wait) you would pronounce it ma'te, with the ' being the little pause.
The small tsu can also appear at the end of a sentence. It is still a glottal stop, leading to a clipped/abrupt end to the syllable it follows, and it acts like an exclamation mark. It occurs a lot in manga, sometimes with an exclamation mark after it too.
In manga especially, other 1/2 sized hiragana can also be encountered, usually in sound effects. These are modulations to the sound effect. This use is non-standard, and often erratic, so as non-natives we just have to imagine from the context what they are supposed to sound like...
Hope that's OK
