Basic Tenses

For past and present, there are 2 non-complex tenses + 6 complex tenses (using auxiliary or helping verbs).

To these, we can add 4 "modal tenses" for the future (using the 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 (though 4 are rarely used).

So now we have 24 tenses, as you see in the table below:

24 tenses past present future
active non-complex tenses past simple present simple future simple
complex tenses past perfect present perfect future perfect
past continuous present continuous future continuous
past perfect continuous present perfect continuous future perfect continuous
passive past simple present simple future simple
past perfect present perfect future perfect
past continuous present continuous future continuous
past perfect continuous present perfect continuous future perfect continuous

The basic structure of a positive or affirmative sentence is:

subject + auxiliary + main verb

The following table shows the 12 active tenses for the regular verb work in the affirmative or positive:

12 active tenses (work) structure past present future
auxiliary main verb
simple normal     I worked I work I will work
intensive do base I did work I do work  
continuous be present participle -ing I was working I am working I will be working
perfect have past participle I had worked I have worked I will have worked
continuous perfect have been present participle -ing I had been working I have been working I will have been working
Notes:

An auxiliary verb is actually used in all tenses. In the present simple and past simple tenses, the auxiliary verb is usually suppressed for the affirmative, but it does exist for intensification. It is also of course always used in forming questions and negatives.

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.