ン ん what is the difference between this 2 ?
Yup! And they use these two main alphabets to distinguish between foreign words and native words. Kanji is used to differentiate between words that sound the same and also because they are usually commonly used. If these answers don't suffice, you can easily search on YouTube "why does Japanese use 3 different scripts?" and get a great answer. :))
I noticed that the course makes no note of the difference between hiragana and katakana. If I didn't already know this I would probably be confused too. The beginning of the course could really use some more explanation about the kana and the different circumstances in which they are used.