The conditional tenses use compound verbs to talk about something happening at a specific time in the present, past or future. These are the verbs that have "ing" endings, and are used with the verb "to be." For past and future constructions, a time reference is given. "Pete is studying"; "Pete was studying at three o'clock yesterday"; and "Pete will be studying tomorrow at three o'clock" are examples of the present, past and future continuous, respectively.
The perfect tenses are compound verbs that are used to talk about something that started at an unspecified time before another event. The auxiliary verb used in this tense is "have," which is used with a participle, such as eaten, been or seen. "John has been here for six days"; "Mark had been in Spain for six months before he left"; and "Michelle will have been here for six months come June" are examples of the present, past and future perfect tense, respectively.
Modal verbs can only be used in compound verbs. Examples of modals are can, could, will, should, could and would. They can be used to make requests, or talk about possibility, as with "can"; to talk about possibility or add politeness, as with "could"; or give advice, as is the case with "should." Not all modal verbs can be used in all tenses. They are used together with participles, as in "Jason could have gone," or with a regular verb, as seen in "Karen can come tomorrow."
The future tense is a compound tense that can take two forms. One uses the auxiliary verb "will" and a main verb. This construction can take the form of a promise, such as "she will help me tomorrow"; or a guess, as in "it will rain tomorrow." Another common way to talk about the future is by using "to be going to" plus a main verb, which is used to convey a plan, such as "John is going to cook dinner tomorrow"; or a prediction, such as "look at the clouds, it's going to rain."
The passive construction is used to emphasize the action of a sentence more than the person doing the action. It is the opposite of the active voice. In this construction, the verb "to be" is used with the past participle, and it can be used in all tenses. "Mike ate a sandwich" is an example of the active voice, while "a sandwich was eaten by Mike" is an example of the passive.