Hi. I'm just gonna say that, because the main point is that I have some questions.

Uhh, what's the difference between transcribing and arranging? Because they seen similar to me.

And, like, what do you define as "basic theory"? Because I don't really know jack of it, beside what I inquisitively ask my director.

Thanks~

Transcribing is directly writing down what you hear and try to keep the original context of a piece of music as close as possible. Meanwhile, arranging is changing its original context or sometimes adding new musical elements into a piece. However, some people consider these terms as synonyms, hence you can sometimes say they're the same.

Well, basic theory can be quite vast depending on what you're talking about. Reading basic notations, understanding basic structures and elements of music (i.e. melodies, rhythms...), and understanding functions of chords are considered basic, in my opinion.