Hi Amine,

there isn't a most used past tense.

We have the tense imperfetto (io ero, tu avevi, lui mangiava, ecc)  to tell or describe an action

ex. Mentre io leggevo, lui guardava la televisione

The tense passato prossimo (io sono stato, tu hai avuto, lui ha mangiato, ecc) is used to express an action in the past but still "felt closed" to us, in the present.

The tense passato remoto (io fui, tu ebbi, lui mangiò, ecc) is used to express an action ended in the past and which doesn't have any effect on our present.

ex. Ho mangiato un'ottima pizza stasera. ---- L'anno scorso mangiai un'ottima pizza in quel ristorante.

There are some differences in the use of passato prossimo  and passato remoto in Italy: northern Italy usually prefers to use the passato prossimo even if the action is completely ended, but these are only regional differences so do not worry :)

I am trying to learn Italian too.... I have been told that the past perfect   (avere + verb in past participle) is the most common for an action that is completely over.    However I noticed with language partners that often C'erano  or C'era is use to describe 'there was or there were'   But other than that.... I have been using a lot of avere + verb  

Hope an Italian teacher will comment :) 

but you use imperfetto also in past situation...

past simple fo english...

for example

i used to do something...

solevo fare questo o l'altro...

facevo questo o l'altro...

different is imperfetto you don't give the same references...

the meaning is always..

I + imperfetto + qualcosa...

when... where..

in other case like duration form... question is since... or for...

imperfetto here is wrong...

ho lavorato a parigi per un anno...

i have been working in paris for one year...

(really action is finishes with passato prossimo so...  i worked... but is for make an example)

in this case traslate lavoravo a parigi per un anno... it's wrong...

because the time is more determinated...

it's hard to exaplain exactly...

i hope you have understand something...

if is not... it's good sign of anarchy...

passato prossimo and imperfetto...

you need only this two past tences in the beginning...focus on it...

other tences are conditonated other actions (two actions connected in the past... etc...), so you can understand better other tences in a sentence than in an explanation...

you can often substituded words in italian..

words are synonyms more than specific words for a specific envoroment...

there is anarchy here in the language.. 

it's something i think teacher dont' teach...

my theory is they are afraid to seem too italian..

verbs are not an exception this anarchy general rule...

(that you have to like.. to smile about... to refuse english way of thinking)

you can chose between passato prossimo and passato remoto for example.. is not wrong... even though grammar could say you to use passato remoto where action is finished and determinated (like simple past)...

but anarchy factor...

how we are saying...

you don't follow the rule...

(this is the main rule... don't follow rules in the language... )

you can use gerundio instead imperfetto....not always... anarchy factor again...

you can chose sometimes between imperfetto and passato prossimo...

if you want to be south italian... pass. remoto...

these three verbs traslate all the past tences in english...

but there is not a rule of traslation...

secret i think is understand what is wrong...

because it's easy two of these verbs (not always the same two verbs) go well...

one is wrong

imperfetto is a time hard to explain...

imperfetto is typicall classic engllish was doing something when something happened...

this situation when you have imperfetto...