I went to a lesson today and got the gist of lazım and felt confident about when to use it.

I came home and looked it up in my grammar book and it said ´see gerek´.

It then said gerek is more grammatically correct.

Now Im really confused as meli /mali are also for necessity..

help!

There are many ways to express necessity in Turkish. Here is an example.

I must go

1)Gitmeliyim.

2)Gitmem gerek.

3)Gitmem lazım.

Just to add my thoughts

In English, I need to, I must, and I have to are very close in meaning.

They all express necessity. 

must = meli/malı suffix

gitmeliyim = I must go

have to = verb root + ma/me + personal suffix, and then lazim

gitmem lazim = I have to go

need to = verb root + ma/me + personal suffix, and then gerekiyor

gitmem gerekiyor = I need to go

there is also similar meanings in

gitmeye mecburum

gitmek zorundayım

thank you, that makes it clearer. My grammar book gave the impression that lazim isnt really used, but it seems it is, and the good thing is the verb endings before lazim and gerek are the same!