Too and enough

Too means "more than is necessary or desirable".

Too + adjective/adverb
This jumper's too big. Can I try a smaller size?

Too much/Too many (+noun)
I can't eat this. There's too much salt in it.
There are too many people there. Let's go outside.

Too + adverb/adjective (+ for + object) + infinitive
It's too cold to play football today.
He spoke too quickly for me to understand her.


Enough means "as much as is necessary"

Adjective/adverb + enough 
Are you warm enough or shall I turn the heating on?

Enough + noun
We'll have to stand because there aren't enough chairs.

Enough (+ for + object) + infinitive with to
I haven't got enough time to see you today.

Let and make

Both these verbs are followed by the infinitive without to.

Let is used to express permission. My dad never lets me watch this movie.


Let is not normally used in the passive. Be allowed to is used instead. I wasn't allowed to go to the party alone.

Make is used to express obligation. The teacher made her do some extra homework.

In the passive, make is followed by the infinitive with to. He was made to pay for the window he had broken.

Permission

To express permission it is possible to use can, may (more formal) or be allowed to. In the negative these express lack of permission, or prohibition.
You can order another drink but you can't have any more hamburgers. 
We aren't allowed to wear trainers to school.

May is not possible in the past. Could and be allowed to are possible for general permission.
In my last job we had flexitime so we could arrive more or less when we wanted to.

Could is not used when referring to a particular situation in the past. Only be allowed to is possible.
I was allowed to stay up late last night.

Obligation and necessity

Must/mustn't + infinitive without to

Must is used:
for strong obligations imposed by the speaker. The speaker uses must to express his/her authority. You must be here by 8 am.
to give strong advice. It's a great film. You really must go and see it.
to tell oneself what is necessary. I must remember to phone Tim.

Must not or mustn't is used:
to talk about something that is not permitted. Passengers must not smoke on the aircraft.
to give strong advice. You mustn't work too hard. You'll make yourself ill.

Past form
Must does not have past form. Had to is therefore used to refer to the past. We had to write a formal letter in the exam. 

Question form
Must is possible in question forms. Must you wear that horrible dress?
although have to is more common. What do we have to do for homework?


Have to/Don't have to

Have to is used to refer to strong obligations imposed by another person rather than by the speaker or writer. I have to be at work by 8 o'clock. The boss will get angry if I'm late.


Need to/Don't need to/Needn't 

Need to is used to express necessity. Can we go to the baker's next? I need to get some bread.


Should/Shouldn't + infinitive without to

Should and shouldn't are used to express obligation or give advice. Ought to can also be used with the same meaning as should. You ought to/should see a doctor about your headache.


Be supposed to/Had better

Be supposed to is used to talk about what you should do because of a rule or because it is expected. Come on, it's 10 o'clock. You're supposed to be in bed!

Had better + infinitive without to is used to talk about what you should do because you think it's a good idea. You'd better ask your dad before you borrow the car.

Do you speak English? - Big train - BBC

Hahahaha, Video without subtitles, but very easy to understand, and very funny!

Monty Python - Four Yorkshiremen

Past tenses

The Past Simple is used to refer to:

Completed actions which happened at a specific time. I went to the cinema last week.
Completed actions and simulations which happened over a specific period of time. I lived and studied in Germany for three years.
Habitual actions or behaviour in the past. We played basketball in the street when I was a child.
A series of consecutive events in the past. He kissed her, said goodbye and closed the door.


The Past Continuous is used to refer to:

Temporary activities or situations in progress at a particular moment in the past. This time last week we were sitting on the beach.
A past activity or situation which was already in progress when another action ocurred (the activity or situation in progress may or may not continue). I was reading to my daughter when the lights went out.
Activities or situations occurring at the same time. Ann was cutting the grass while I was cooking.
The background events in a narrative. It was snowing heavily and a cold wind was blowing. 


The Past Perfect is used to:

Show that a past action or situation occurred before another past action or situation. When I saw Tom, he had just passed his driving test.
We used the continuous form to enphasize the duration of the first past action or situation. She had been waiting  for over two hours when he phoned to say he couldn't come.


Time linkers:

The past perfect is often used with time linkers. ex: after, before, by the time, as soon as, once, when, until. I couldn't go out until I had done my homework.

The past simple can be used if the order of events is clear. He sold his house before he left the country. Or if the second event occurred as a result of the first. When I realized what time it was, I ran outside.

After/afterwards. 
After is used to show the order of two or more events in the same sentence. Afterwards means "after that" and can go at the beginning or the end of a clause.

At last/in the end/at the end.
At last suggest that something good happends after a long period of time or more than one attempt.
In the end has a similar meaning and may also suggest there have been one or more changes or problems. They result may be good or bad.
At the end means at the point when something finishes.

When/as/while.
These can all be used with the past continuous to introduce an action which was already in progress when another action occurred.

During/in/for.
These are all used as prepositions when referring to time, and are followed by a noun. During and in are used to say when something happened. For is used to say how long something took or lasted.