when to use verbs in the past and when to use "did" ?
i don´t understand sometimes use "did" in the past tense, but other times the people use verb in past tense?

Question

Answer

Use "did" in the past for questions or negatives, when you are giving a short answer or when you want to be emphatic (adding emphasis).
Examples:
Did you eat? (question)
Yes, I did.  (Short answer)
No I did not eat. (negative)
You didn't eat?  Yes, I did eat.  (emphatic)
Hope this helps.

Answer

The use of did is generally always a past tense confirmation or in a question. (Have you eaten? I did/did not) (Did you eat?) It's a slightly odd word in general and I'd feel it is generally a slang word but so commonly used it became a staple in casual speech.