2. Usage
Corresponds best to English:
“I was doing something” - has to be a continuous action or state that lasted
for a certain amount of time. Compare with the Preterite, which is for a
single event.
e.g. mientras jugaba, se cayó al suelo
While he was playing, he fell to the floor.
“Playing” is a state or an action that was happening for quite some time, and so
we use the Imperfect. But the “fell” to the floor action interrupts this. It's
sudden, and short, and so it is a Preterite.
3. Usage
Corresponds best to English:
“I used to do something/ I would” - in English, I “would” can refer to the
past as well as being a conditional. Think about what you “would” do in your
early morning routine at school years ago.
e.g. todas las dias, me levantaba a las 6.
Every day, I would get up at 6/ Every day I used to get up at 6.
Although the “getting up” is a single, short-lived action, we use the Imperfect
here instead of the Preterite, because it is repeated over a long period of
time!