THE USE OF DO TO AVOID REPETITION OF A PREVIOUS VERB

The auxiliary DO is used in different tenses and forms (did, does, didn't) to avoid repeating the verb used in the previous sentence.
Mother: Who made the cake?
Daughter: I did, Mom.
"I did, Mom." - instead of - "I made the cake, Mom."

1-Mary travels 10 hours a day. I don't know how she does it.
2-Most of the children came yesterday; just a few didn't.
In the fist case, DO is used as a full verb with the sense of performing an activity or task.
In the second case, DO is used as an auxiliary verb.
In both cases, do is used to avoid repetition of a previus verb.

DO is never an auxiliary when it's immediately followed by an object.
Don't forget to look over your class notes, Paul.
I've already done it, Mom.

TIMES OF FUTURE

THE FUTURE PERFECT TENSE

The form is:
SIMPLE FUTURE OF "TO HAVE" + PAST PARTICIPLE OF THE MAIN VERB

The Future Perfect Tense refers to a completed action in the future. Is used in conjunction with such expressions as by the time, by this time, or by.
By the time we get there, the movie will have already starded.

The expression by the time can introduce either a past or a future idea.

The Future Perfect Tense refering to a completed action in the future is also used in clauses following such a verbs as believe, expect, hope, suppose or expressions of certainty.
I'm pretty sure she'll have received my envelope by the end of this week.

THE INTERROGATIVE FORM OF THE FUTURE PERFECT TENSE
How much will I have spent on clothes by September?

THE NEGATIVE FORM OF THE FUTURE PERFECT TENSE
I will not have spent on clothes by September.
I won't have spent on clothes by September.

BY THE TIME
This expression can introduce either a past or a future idea:
By the time we get there, the soap-opera will have already started.
By the time we got there, the soap-opera had alread started.
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EXPRESSING FUTURE

What's difference between the use of the GOING TO Future and the Simple Future with WILL?

1-SIMPLE FUTURE WITH WILL: expresses a future action or state of being in which the element of certainty is not present:
I will travel to Paris next year. (If I have the time, the money, etc...)

2-GOING TO FUTURE: expresses a future action or state of being in which the element of certainty is present:
I'm going to travel to Europe next year. (I'm determined to go and I'm alread doing what is necessary to realize my future action).

PRESENT CONTINUOUS TENSE AND GOING TO FUTURE
They can be used to refer to a future event in which the element of certainty is present.
Paul is seeing the doctor next monday - or - Paul is going to see the doctor next monday.

SIMPLE PRESENT TENSE
It's can also be used to refer to a future event that will as part a program, or as part of as series of events that routinely take place. An adverb( like: tomorrow) or an adverbial phrase (like: next week, in three hours, ..) is usually combined with the Simple Present Tense.
Next week, he celebrate his 15th years old.

PASSIVE VOICE

The passive voice is used when we don't know or when it's not important to know who or what performed an action.

PRESENT CONTINUOUS TENSE
The form is:
THE PRESENT CONTINUOUS TENSE OF THE VERB TO BE + THE PAST PARTICIPLE OF THE MAIN VERB
Brochures are being sent to all of the agency's custumers.

PAST CONTINUOUS TENSE
The form is:
THE PAST CONTINUOUS TENSE OF THE VERB TO BE + THE PAST PARTICIPLE OF THE MAIN VERB
Brochures were being sent to all of the agency's custumers.

PRESENT PERFECT TENSE
The form is:
THE PRESENT PERFECT TENSE OF THE VERB TO BE + THE PAST PARTICIPLE OF THE MAIN VERB
Brochures has been sent to all of the agency's custumers.

PAST PERFECT TENSE
The form is:
THE PASTPERFECT TENSE OF THE VERB TO BE + THE PAST PARTICIPLE OF THE MAIN VERB
Brochures had ben sent to all of the agency's custumers.