The new classes have not started yet but, I am going though the lessons slowly by myself and I am hoping someone can clarify something form me.

In the below example:

araba-in -> araba-n-ýn -> arabanýn (of the car, the car´s)
konu-in -> konu-n-un -> konunun (of the topic)

I understand what the addition of ---in does and why it changes form (due to vowel harmony)What I do not understand is why the addition of the extra "n" between the actual noun and the sufix "...in"

In Turkish, when you add a suffix beginning with a vowel to a stem that ends in a vowel, you need to add a consonant between them - I guess it´s easier to pronounce that way. Those consonants, that are used to separate two vowels between stem and suffix, are called buffer letters. There are 3 buffer letters used in Turkish: s, y, and n. Doudi posted a nice explanation of the rules when to use which buffer letter, so I´m just going to copy and paste it here:

"You use s :

-for possessed endings

-compound nouns

You use n:

-for possessor endings

-with a word that already has a possessed ending

-with personal pronouns bu, þu and o
-with -ki ending

other than that use y"

So in your example, the "n" letter was used because a "possessor" suffix was attached and it was added in order to prevent 2 vowels from occurring together: konuun or arabaýn would be awkward to pronounce.

Let me also illustrate it on the word araba:

you use s :

-for possessed endings - arabasý (his/her car),

-compound nouns - Türk arabasý (Turkish car)

You use n:

-for possessor endings - arabanýn renðý (the car´s color)

-with a word that already has a possessed ending - arabasýnda - araba-s-ý-n-da (in his car)

-with personal pronouns bu, þu and o - bunu, þunu, onu, etc
-with -ki ending - hmmm, not sure what example to give here

other than that use y - arabayý çok seviyorum

Hope those above will be a help for you.