For past and present, there are 2 simple tenses + 6 complex 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. So now we have 24 tenses.
Some grammar books use the word progressive instead of continuous. They are exactly the same.
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:
subject + auxiliary verb + main verb
An auxiliary verb is used in all tenses. (In the simple present and simple past tenses, the auxiliary verb is usually suppressed for the affirmative, but it does exist for intensification.) The following table shows the 12 tenses for the verb to work in the active voice.
* 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.