What is the difference between 나를 and 나는 and 당신 and 당신은 ?Feel free to just provide example sentences.

Many study books say English 'you' is '당신' in Korean.
But this is a big mistake.
I do not think this big mistake is due to editor's carelessness.
This mistake is due to Korean language's character.
English 'you' covers almost all cases, but there is no word exactly equivalent to English 'you' in Korean.
너 is close to 'you' but 너 can be used to friends or familiar younger people than the speaker. 너 is informal or casual.
There is no word equivalent to 'you' which can be used to older people or higher ranker than the speaker.
Koreans use hearer's position, not 당신 to imply 'you' when the speaker says to older people or higher ranker, or unfamiliar younger people.

Ex)
Are you tired, dad? => 아빠 피곤하세요?
There is no saying 'you' (in Korean), is just position 아빠. (There is no saying 당신.)
The Korean language has many words to imply 'you' (in Korean) instead of '당신': 선생님, 부장님, 사장님, 어르신, 이모, 언니, 학생, 젊은이, 기사님.

당신(You) is used only between spouses(wife & husband), otherwise, they(Not spouses) usually use 당신 when they are angry. It is ironic that 당신 is used both in soft situations (Between spouses or wife & husband) and stomy situations (Between arguing people), but it is real and true.
당신 can be impolite(informal) sometimes even though 당신 is formal.

(From Astrophil's answer):

We(They) usually add 씨 after his/her name and/or 님 after a position.

Maria => 마리아씨
Bongwoo => 봉우씨

To a teacher: 선생님
To a professor: 교수님

And we(they) usually say 선생님 to a stranger who looks older than the speaker. It doesn't have to do with a teacher.

그대 is like, an old and (very) formal word, not used in life. It has been used in a poem, lyrics... etc.

자네 is used when older person calls younger person "자네". 자네 is 하게체 style, which means familiar style.