Double-click on any word and see its definition from Cambridge Dictionaries Online.

1. What's the difference between till and until?

until, till (TIME) preposition, conjunction: up to (the time that)

			I was up until three o'clock trying to get it finished!
			Wait till you see what Rachel's wearing!
			Hadn't we better wait until Antony's here?

until, till (DISTANCE) preposition, conjunction : as far as

You should stay on the train until/till Manchester and then change.

http://dictionary.cambridge.org/

Till is slightly more informal. When used at the beginning of a sentence, we would usually use until:

Until they arrived, everything was fine. (NOT Till they arrived …)

The word till also has the following completely different meanings:

till, American usually register (MONEY DRAWER) noun: the drawer in a cash register a machine in a shop which records sales, and in which money is kept, or esp. Br informal a cash register

Next time you have the till open, could you give me some change?

till (PREPARE LAND) verb: to prepare and use (land) for growing crops

This piece of land has been tilled for hundreds of years.

http://dictionary.cambridge.org/

2. What's the meaning of "affirmative statement"?

In grammar, when we are describing verb tenses, we talk about the affirmative, the negative and the interrogative (or question). For example, the 2nd person singular for the present simple is:

Affirmative: you work
Negative: you don't work
Question: Do you work?

In other contexts, an affirmative statement basically means that the speaker (or writer) said "Yes" (or meant "yes").

			A: Are you coming with us?
			B: OK. That'd be good.

" OK. That'd be good." is an affirmative statement.

3. What can he and she refer to in English?

In some languages, every object or thing (be it concrete or abstract) has a gender, i.e. it is masculine or feminine. This is not the case in English, where people are he or she, and things are it.

The only real exceptions are animals (especially pets) and vehicles such as ships, cars and motorcycles. Most people refer to their pets as he or she, because they think of them as having more of a personality than "just an animal". The same sometimes applies for farm animals, and even animals in a zoo. Sailors usually refer to ships as she. Proud owners of cars and motorcycles may also do this, although in these cases most people would use it.

More on gender in English:

http://www.edufind.com/english/grammar/NOUNS1.cfm

http://www.english.upenn.edu/~cjacobso/gender.html

4. what is syntax?

Curiously, although this is actually a very complex question on one level, it is possible to give a basic answer on another level. It is not difficult to understand what syntax is, but it is very difficult to understand syntax!

Syntax noun SPECIALIZED: the grammatical arrangement of words in a sentence

http://dictionary.cambridge.org/

Main Entry: syn.tax
Pronunciation: 'sin-"taks
Function: noun
Etymology: French or Late Latin; French syntaxe, from Late Latin syntaxis, from Greek, from syntassein to arrange together, from syn- + tassein to arrange
Date: 1574
1 a : the way in which linguistic elements (as words) are put together to form constituents (as phrases or clauses) b : the part of grammar dealing with this

http://www.yourdictionary.com/

Explaining the syntax of the English language is way beyond the scope of this article. If you are interested, see:

http://faculty.washington.edu/dillon/GramResources/GramResources.html

5. What is the origin of the word OK?

http://www.datasync.com/~rsf1/ok.htm

6. When we can change who for that?

Who and that, as well as which, whom and where, are relative pronouns, and are used in relative clauses. The basic rules of relative clauses are explained in our section on Grammar Definitions. It mentions two types of relative clause: identifying (also known as defining) and non-identifying (non-defining). In identifying relative clauses we can substitute who for that. In non-identifying relative clauses we cannot.

identifying (defining)

The actor who/that lives in London is in town at the moment.

(the actor is identified - we know which actor is being talked about)

non-identifying (non-defining)

The actor, who lives in London, is in town at the moment.

(here we are given some extra information about the actor)

More on relative pronouns and clauses:

http://www.edufind.com/english/grammar/rel4.cfm

7. What is the meaning of ye?

ye (YOU) pronoun OLD USE: (used when addressing more than one person) you

			Ye cannot serve God and mammon.
			I'll fetch the master for ye.

http://dictionary.cambridge.org/

Main Entry: ye
Pronunciation: yE
Function: pronoun
Etymology: Middle English, from Old English gE; akin to Old High German ir you
Date: before 12th century
used orig. only as a plural pronoun of the second person in the subjective case and now used especially in ecclesiastical or literary language and in various English dialects.

http://www.yourdictionary.com/

8. Is it possible to write "How are u? "?

In "normal" written English this form is not really acceptable. It comes from the language of text-messaging, in which abbreviations are used wherever possible, and is common when sending text messages via mobile phones, on internet chat and in informal e-mail messages. In fact, the question above would probably be abbreviated to "How RU? ".

9. How do we say numbers like "8.83"?.

In English, the dot in numbers with decimals places is said as point:

			Eight point eight three = 8.83
			Fifty-five point four two = 55.42
			A hundred and six point nine seven = 106.97

More on numbers:

http://www.edufind.com/english/grammar/Determiners10.cfm