What purpose does يا serve?
it's a "proposition" that works as punctuation to point someone in a friendly and unfriendly way.
it can be used like :
Mike! or Hey Mike!
for addressing to a person
In English, people say "hey" before someone's name as a call to attention as in "hey mike" just as in Arabic it is said as "oh Mike".
What is the difference between مُعَلِّم (teacher) and أُسْتاذ (professor)?
In English, a teacher is anyone who teaches: at school, at church, or in a community class. A professor is usually at a college level and has usually reached a higher level of education. I don't know if it has the same distinction in Arabic or not.
Article A is overrated -_-
How would the same sentence translate in the past or future tense in arabic?
كنت معلماً يا مايك
ستكون معلماً يا مايك