The most importand conjunctions (BAĞLAM = BAĞLAÇ) in Turkish Language=

VE
İLE
AMA
FAKAT
ÇÜNKÜ
BAZAN
VEYA = YA DA
İÇİN
ŞAYET = EĞER
YOKSA
AKSİ TAKDİRDE
ÖYLEYSE
ŞİMDİ
BUNA GÖRE
YANİ
OYSA
DEMEK Kİ
YAHUT
NİTEKİM
HALBUKİ
GERÇEKTEN
O ZAMAN
BU SEBEPLE
BUNUN ÃœZERİNE
YİNE DE
BİLE
ZATEN
NASIL Kİ
ŞU VAR Kİ
AMA NE VAR Kİ
KALDI Kİ
OYSA Kİ
YALNIZ
BUNDAN DOLAYI
BU NEDENLE
HAL BÖYLEYKEN
GEREK...GEREK - GEREKSE- ...
HEM...HEM...
NE...NE...
...OLSUN...OLSUN
KİMİ
ÖBÜRÜ
İSTER...İSTER...
LAKİN
ŞAYET
ÃœSTELİK
BİLE
YETER Kİ

Some of them are not conjunctions (bağlaç).

Kitap = Türkçenin Grameri (2007 Baskısı
Yazarı = Tahsin Banguoğlu
Yayınlayan= Türk Dil Kurumu

Bağlam = Sayfe = 391
Sayfa = 392
8.paragraf
Yerverme bağlamları=
GERÇEKTEN
NETEKİM
HALBUKİ
OYSA
HAL BÖYLEYKEN

SAYFA 391= ULAMA BAĞLAMLARI=
İLE
VE
DE
..

WE USE İT AS " NİTEKİM "

"TÃœRKÇENİN GRAMERİ" USES IT AS "NETEKİM"

BUT "İMLA KILAVUZU" USES IT AS "NİTEKİM"

Hey hocalarmız ...
How about a little explanation for each ?!

thanks for the correction caliptrix ... Oops got one wrong

AKSİ TAKDİRDE: Otherwise
Literally: on the opposite situation

Lütfen sessiz olun, aksi takdirde polis çağıracağım.
Please be quiet, otherwise I will call the cops.
This one is found mostly on legal documents and product warnings but also used on everyday speech. In informal speech, YOKSA(or/or else) is used instead.
Ondan özür dile yoksa kafanı kırarım.
Apologize to her or I'll bash your head.
YOKSA has many meanings, but that's another story..


ÖYLEYSE: In that case/Therefore
Literally: If it(the case) is like that / If that is the case

- Lavoboyu tamir edemiyorum / I can't fix the sink.
- Öyleyse tesisatçıyı çağırıyorum. / In that case, I'm calling the plumber.
DüşÃ¼nüyorum, öyleyse varım.
I think, therefore I exist.


BUNA GÖRE: According to this.
GÖRE is usually used on its own:
Bilim adamlarına göre küresel ısınma ciddi bir tehdit.
According to the scientists global warming is a serious threat.
Haritaya göre sağa dönmeliyiz.
According to the map, we should turn right.


OYSA: However/Yet/But
Used between two opposing sentences:
Doktor sigara kanser yapar dedi oysa kendisi günde bir paket içiyor.
The doc said smoking causes cancer but/yet he smokes a packet a day.


DEMEK Kİ: So/therefore/thus
Literally: It(the situation) means that/That means/That is to say

DüşÃ¼nüyorum, demek ki varım.
I think, therefore I exist.
This has exactly the same meaning as "DüşÃ¼nüyorum, öyleyse varım".
The first sentence presents an observation or situation + "öyleyse" or "demek ki" comes next + then the second sentence draws a conclusion from the first one.

But consider the following example:
Ahmet: "Işık yeşil yanıyor." / The light is green.
Mehmet: "Öyleyse gaza bas!" / So(in that case) step on the gas!
is CORRECT. But:

Mehmet: "Demek ki gaza bas!" is gramatically INCORRECT. Here Mehmet should say:
"Demek ki gaza basmalısın"
Literally: "It (the green light) means you should/need to step on the gas!"

A similar exaample:
Matematik sınavından kaldım, demek ki daha çok çalışmalıyım.
I failed at mathematics, (to wit/That is to say that) I should study harder.

Confused yet?
More to come hopefully...

Ok,first question,
İ see that there are many conjunctions are similar to the others
So is it a personal prefrence when to use each one ?!
Like
Ama,Lakin,Halbuki,yalnız...but
Veya,YAHUT,ya da...
Or each has its own pereferable usage ?!

Second,
How do we form sentences from
GEREK...GEREK - GEREKSE- ...
...OLSUN...OLSUN
İSTER...İSTER...
Do they came in same sentence ,i mean do we for example use GEREK...GEREK - GEREKSE- in one sentence ,and OLSUN...OLSUN in one sentence...ect ?
How ?

Third,
Regarding to "öyleyse" and "demek ki"

Can we say,its preferable that we use imparitive with öyleyse and use 'malı ' suffix with demek ki ?

Ok,first question,
İ see that there are many conjunctions are similar to the others
So is it a personal prefrence when to use each one ?!
Like
Ama,Lakin,Halbuki,yalnız...but
Veya,YAHUT,ya da...
Or each has its own pereferable usage ?!
---------
It's a shame I don't know the exact answer. Maybe because it's 2am here and I'm really tired. Then maybe there is no exact answer.
Yes, looks like it all comes down to personal style, context and something else that I dunno.

AMA means "But". Most frequently used one.
Between two conflicting sentences:

'Sigara içmeyin' diyor ama kendisi içiyor
She says 'Don't smoke' but she smokes herself.
could be written with LAKİN or HALBUKİ or ANCAK, instead of ama!
And I cannot tell any difference except lakin sounds old-fashioned! When in doubt use AMA!

YALNIZ has a different use:
Etrafı gezebilirsiniz YALNIZ hiçbirşeye dokunmayın.
You can look around BUT don't touch anything.= On the condition that you don't touch. Remember YALNIZ also meaans ONLY, and to avoid ambiguous situations you may choose not to use it at all.
Etrafı gezebilirsiniz AMA hiçbirşeye dokunmayın. means just the same.

VEYA, YAHUT, YA DA each may be used. YAHUT and YA DA come from Farsi I think. YAHUT sounds a bit old-fashioned.
2 ya da/yahut/veya 3 bardak raki içtim
I had 2 or 3 glasses of raki.

Second,
How do we form sentences from
GEREK...GEREK - GEREKSE- ...
-----------
open seslisozluk.com
search for "gerek" & look at 4th and 5th examples.

olsun...olsun and ister..ister are used similarly:
Elma olsun, portakal olsun severim.
I like BOTH apple(s) and orange(s).

Ahmet olsun Mehmet olsun çalışkan elemanlarımızdır.
BOTH Ahmet AND Mehmet are our hard-working staff.

Ayşe İngilizceyi olsun, Fransızcayı olsun iyi konuşur.
Ayşe speaks BOTH English AND French well.
could be expressed as:
Ayşe gerek İngilizceyi, gerek(se) Fransızcayı iyi konuşur.

İster...ister comes from istemek, to want:
İster trenle, ister otobüsle git.
EITHER go by train OR by bus. (Whichever way you want)

İster bugün ister yarın gel.
İster bugün gel ister yarın.
Come (either)today or tomorrow. (whenever you like)

Third,
Regarding to "öyleyse" and "demek ki"

Can we say,its preferable that we use imparitive with öyleyse and use 'malı ' suffix with demek ki ?
-----------------

If you intend to use an imperative then you cannot use DEMEK Kİ. No direct orders may come after "demek ki". Only conclusions may follow.
Eg:
Ahmet says "The room is dark, I cannot see anything"
Mehmet may answer:
Öyleyse ışığı aç
O zaman ışığı aç
O halde ışığı aç
All means "So, turn on the light!" issuing a direct command and all are perfectly valid. Use whichever you like.
But the answer
"Demek ki ışığı aç" is NOT valid. Literally this sentence says "That is/That means/It follows, turn on the light"

You can say
"Demek ki ışığı açmalısın"
"Then you must turn on the light"(It follows that you must turn on the light)

However, do not assume that an obligation suffix (-meli) must come after "demek ki". Another example:

Zil çalıyor./The bell is ringing.
O zaman ders bitti / So(in that time/Then), the lesson is over
O halde ders bitti / So(in that situation), the lesson is over
Öyleyse ders bitti / So(if that is so), the lesson is over
Demek ki ders bitti / It follows that, the lesson is over

No -meli needed after "demek ki". Just no direct orders. All are valid, but demek ki has a slightly different meaning and use. Nevermind. I don't like it anyway
Just don't forget that O ZAMAN, O HALDE, ÖYLEYSE have the same meaning. Now you may ask, if they are all the same, why have seperate words? I'll be damned if I know!

Ask again, and you will (hopefully) receive -an answer.

Thank you lazy42,you are very much helpful