One way to form the simple future tense in the English language is to use the auxiliary verb "will" or "shall" in front of the base form of the verb. The sentences "He will study for the test tonight" and "I shall ask her tomorrow" both convey future tense.
Another common way to indicate an action that has not yet happened is to combine a form of the verb "to be" with the verb "going" and place them in front of the infinitive form of the verb. Such an example is "Jane is going to bake the cake this afternoon."
Combining a form of "to be" with the infinitive form of a verb can also indicate future tense. The sentence "You are to leave by five" shows such a construction.