Io dico, o io ho detto
Mi scusi, I need to ask in English.
In English if you are telling a story about the past, you can speak as if it is were the present. What is the best tense to tell a story that happened in the past in Italian?

Can I say "Io dico...

or do I have to say "Io ho detto..?

Question

Io dico, o io ho detto
Mi scusi, I need to ask in English.
In English if you are telling a story about the past, you can speak as if it is were the present. What is the best tense to tell a story that happened in the past in Italian?

Can I say "Io dico...

or do I have to say "Io ho detto..?

Answer

Anche in italiano si può usare il presente per esprimere il passato. Viene chiamato presente storico. 
Nei romanzi si usa spesso l'imperfetto, ma viene alternato con le altre forme del passato (passato prossimo, passato remoto e qualche volta trapassato remoto).

Esempio con presente storico: è una storia che inizia molto tempo fa. Nel 1989 cade il muro di Berlino e finisce il vecchio mondo ....

Answer

If you are in an informal conversation it's ok to say the story in present tense. But to be more correct, usually we use Passato Prossimo (ho detto, sono andato...) for finished actions, and Imperfetto (dicevo, ero, andavo...) for descriptions, vague time, repeated actions.
In novels, you will mainly find the Passato Prossimo replaced with Passato Remoto (dissi, andai...)

I can see that you have a beginner level, maybe it's better for you to use present tense for now, simpler and making sure the grammar is correct. You can learn the past later. Just my advice.