Present
Present tense is used, in principle, to refer to circumstances that exist at the present time (or over a period that includes the present time) and general truths. However the same forms are quite often also used to refer to future circumstances, as in "He's coming tomorrow" (hence this tense is sometimes referred to as present-future or nonpast). For certain grammatical contexts where the present tense is the standard way to refer to the future, e.g., conditional sentences and dependent clauses. It is also possible for the present tense to be used when referring to no particular real time (as when telling a story), or when recounting past events (the historical present, particularly common in headline language). The present perfect intrinsically refers to past events, although it can be considered to denote primarily the resulting present situation rather than the events themselves.
The present tense has two moods, indicative and subjunctive; when no mood is specified, it is often the indicative that is meant. In a present indicative construction, the finite verb appears in its base form, or in its -s form if its subject is third-person singular. (The verb be has the forms am, is, are, while the modal verbs do not add -s for third-person singular.)
Past
Past tense forms express circumstances existing at some time in the past, although they also have certain uses in referring to hypothetical situations (as in some conditional sentences, dependent clauses and expressions of wish). They are formed using the finite verb in its preterite (simple past) form.
Certain uses of the past tense may be referred to as subjunctives; however the only distinction in verb conjugation between the past indicative and past subjunctive is the possible use of were in the subjunctive in place of was.
Note also that in certain contexts past events are reported using the present perfect.
Future
English is sometimes described as having a future tense, although since future time is not specifically expressed by verb inflection, some grammarians identify only two tenses (present or present-future, and past). The English "future" usually refers to a periphrastic form involving the auxiliary verb will (or sometimes shall when used with a first-person subject). There also exist other ways of referring to future circumstances, including the going to construction, and the use of present tense forms. For particular grammatical contexts where the present tense substitutes for the future, see conditional sentences and dependent clauses. For discussion and comparison of the various ways of making future reference in English, see going-to future.
For specific uses of future constructions formed with will/shall, see future.
Future-in-the-past
A "future-in-the-past" tense (or form) is sometimes referred to. This takes essentially the same form as the conditional, that is, it is made using the auxiliary would (or sometimes should in the first person).
This form has a future-in-the-past meaning in sentences such as She knew that she would win the game. Here the sentence as a whole refers to some particular past time, but would win refers to a time in the future relative to that past time.