Tense
Tense (from The Concise Oxford Dictionary) (noun Gram.): Form taken by a verb to indicate the time(also continuance or completeness) of an action …in relation to the time of speaking. (From Latin tempus = time).

Tense is a method that we use in English to refer to time—past, present and future. Many languages use tenses to talk about time. Other languages have no tenses, but of course they can still talk about time, using different methods.
So, we use tenses in English to talk about time. But, and this is a very big but:
we can also talk about time without using tenses (for example, going to is a special construction to talk about the future, it is not a tense)
one tense does not always talk about one time.
Here are some of the terms used in discussing verbs and tenses.
Tense and Time
It is important not to mistake the name of a verb tense with the way we use it to talk about time.
For example, a present tense does not always refer to present time:
I hope it snows tomorrow: "snows" is a present simple, but here it refers to future time (tomorrow).
I go to Rome two days a month: “go” is a present simple, but it doesn’t mean I am going now to Rome.
Or a past tense does not always refer to past time:
If I had some money now, I could buy it:"had" is a past simple but it refers here to present time (now)
There are 24 tenses. For past and present, there are 2 simple tenses + 6 compound tenses (using auxiliary verbs). To these, we can add 4 "modal tenses" for the future (using modal auxiliary verbs will/shall). This makes a total of 12 tenses in the active voice. Another 12 tenses are available in the passive voice.
The use of tenses in English may be quite complicated, but the structure of English tenses is actually very simple. The basic structure for a positive sentence is:
positive:
+

subject( + auxiliary verb) + main verb
(soggetto -+verbo ausiliare-+verbo principale)
negative:
-

subject + auxiliary verb + not (+ main verb)



(soggetto +verbo ausiliare+not-+verbo principale-)
question:
?

auxiliary verb + subject (+ main verb)
(+verbo ausiliare+ soggetto -+verbo principale -)

An auxiliary verb is used in all tenses. (In the simple present and simple past tenses, the auxiliary verb is usually abolished for the affirmative, but it does exist for intensification.)
Technically, there are no future tenses in English. The word will is a modal auxiliary verb and future tenses are sometimes called "modal tenses". The examples are included here for convenience and comparison.
Some grammar books use the word progressive instead of continuous. They are exactly the same.
The basic structure of tenses for regular verbs and irregular verbs (bare form) is exactly the same (except to be). The only difference is that with regular verbs the past and past participle are always the same (played, played), while with irregular verbs the past and past participle are not always the same (wrote, written). But the structure is the same! It will help you a great deal to really understand that.
To be continued