I have a question about the phrase "have to"
For example according to --Learn turkish--- I have to work now is:
Şimdi çalışmam lazım.
But when I asked my friend from Turkey how to say it he said:
Şimdi çalışmam zorundayım.

who can explain me the difference between them??

Şimdi çalışmak zorundayım.
Şimdi çalışmam lazım.

Same meaning, different usage. By the way, "zorunda" sounds more "an obligatory comes from a higher authorithy"

I need to work: Çalışmam lazım or Çalışmam gerekiyor or Çalışmalıyım

I have to work: Çalışmak zorundayım

If this is a work that your boss is near to you and observes always you, so you have to be there and have to work. Here, zorunda is good.

But if this is a study, and you need to study to graduate the school, then it seems more "your choice". Then you may say: I must study. Here, both zorunda and lazım sounds good.

Çalışmam lazım=Çalışmalıyım.(I must/should)
Çalışmak zorundayım.(I have to)

A friend of mine told me that 'Lazım 'was OLD turkish and not used very often so he saıd that I should prefer 'gerek/ gerekiyor' ınstead . For example:
I have to go = 'gitmem gerek' and not 'gitmem lazım'.
Is he rıght? ıs 'Lazım' not used very often to express oblıgatıon?
greetıngs.
Dilara.

There are some differences between the two. Gerekmek is a verb while lazım is an adjective. Gerekmek (to be needed) can be used in different tenses. Therefore it has a wider range of use. There are possible versions such as gerekmektedir, gerekiyor, gerekir etc. These are used in written and formal language as well. Especially gerekmektedir is part of written language only. Of course we also have the adjective version of gerekmek which is 'gerekli' (needed).

In formal speech 'gerekmek' is slightly better. For instance it is better to say "gelmeniz gerekiyor", "gitmeniz gerekiyor", "aramanız gerekiyor".

On the other hand in informal speech 'lazım' can be slightly better: "gelmen lazım", "gitmen lazım", "araman lazım".

"Benim şimdi gitmem gerekiyor" (with the present continuous tense suffix) sounds slightly more polite and slightly more educated than "Benim şimdi gitmem lazım". Gerekmek keeps the distance while lazım sounds more informal.

There is also a small difference in meaning between lazım and gerekli or any version of gerekmek. We can say "ekmek lazım" (we need bread) or "su lazım" (we need water) to point out to something that lacks. There is no smillar usage of gerekmek or gerekli.

For instance this sentence is very common: "Bir şey lazım mı?" (Do you need something?). It is part of everyday speech among people who know each other. There is no version with gerekmek that can be as informal.

Actually it is quite usefull to learn a langauge with common sentences such as "benim şimdi gitmem gerekiyor" and "bir şey lazım mı". You gain a feeling where to use what word.