What the point of using 'do/does/did' in pozitive sentences?
Hello. I encountered the case when 'do/does/did' were used in POZITIVE sentences. Will you be so kind to explain me what it's for? Here are some examples: 'You did tell me', 'I do like to eat cereal in the mornings', 'He does study English on Fridays'.
I know, that these verbs are necessary in negatives or questions, e.g., 'They don't want to be doctors' or 'Does he work as a teacher?'. As for pozitives sentencers, I can't see the point of these verbs using.
Thank you in advance.

Question

What the point of using 'do/does/did' in pozitive sentences?
Hello. I encountered the case when 'do/does/did' were used in POZITIVE sentences. Will you be so kind to explain me what it's for? Here are some examples: 'You did tell me', 'I do like to eat cereal in the mornings', 'He does study English on Fridays'. 
I know, that these verbs are necessary in negatives or questions, e.g., 'They don't want to be doctors' or 'Does he work as a teacher?'. As for pozitives sentencers, I can't see the point of these verbs using.
Thank you in advance.

Answer

You cannot see the point of using "do" in positive sentences ? Well, it is used to emphasize the reality of the thing mentioned. For example : "nobody told you to" Answer "you did tell me" ; "only old people eat cereals in the morning". Answer (from a young man/woman probably) : "Well, I do like to eat..."

Answer

I'd say it's grammatically correct adding "do". Let say: "I like him" or "I do like him" are basically the same. Except that the "do" part adds emphasis, and is usually a way to counter what the other person said.
-You don't want this!
-Yes, I do want this!.

Answer

"Do" is used to insist or to emphasize or to correct.

(neutral)
I exercise.  I walk the dog every day.

(insistant)
- "Darling, you should exercise more."
- "But I do exercise.  I walk the dog every day!"