Be not confused.
The woeful truth is, you have, for too long, dwelled under the misconception that WHAT you say and HOW you say it make little difference.
You are mistaken. Both are critical. How people perceive you is directly related to both the words you say and your use of them. (Your appearance is ALSO a crucial element of the impression you present. Clothes make the individual.)
Consider the following: "I didn't say she stole money." Read it six times. Emphasize a different word each time. Note how the connotation changes. My point, exactly.
Upon your arrival in my classroom, you should be aware that you have pressed "1 for English", metaphorically. There really are no options. It matters not who you are or which class you are taking. I have taken a solemn oath to do my level best to prepare you for college and for a world hungry to be impressed by well-spoken individuals. The oath, paraphrased, states that I shall instruct and correct you, tirelessly. (Think of me as Henry Higgins, if you must.)
I have no motive for providing you with erroneous information, so we shall not argue when you proclaim, "That don't sound right." Trust me when I tell you what it is you should be saying and how you should be saying it. To do so otherwise will, naturally, impact your future . . . and your grade.
I suspect you knew the latter might be forthcoming.
Mr. Steve Merritt