Quote Originally Posted by M.Vonok View Post
1. I do not confidently understand the use of "дело" in this context, is it correct to translate this as "But the concern is that I know for sure you speak English very well?"
Но дело в том, что я знаю хорошо, что вы говорите отлично по-английски
"Дело" here means "cause, problem, matter, keypoint". "Дело в том, что..." is something like "the matter is...".

Quote Originally Posted by M.Vonok View Post
2. I do not understand ''То есть," and if this is translated as "my aunt took me to the tutor" why does it not employ a preposition such as "моя тетя взяла мне в/к репетитор-a/y?" I am confused here...
То есть моя тетя взяла мне репетитора....
No, it is not translated "my aunt took me to the tutor". It is "my aunt took me a tutor", here "репетитор" is in accusative. So, it is like "she took (hired) a tutor (for) me".

If you want to say "my aunt took me to the tutor", it would be "Моя тетя взяла меня к репетиторy". Note: it would be "меня" (accusative), not "мне" (dative). The preposition "в" is impossible with persons, since "в" means "into", "to the point inside something".