how to use "if" in lisp

[Teng Wang]

Hi there,

I just began to learn lisp a couple of weeks ago. It is easy to use,
but sometimes it is really hard to know what variables are in
lisp. And today I want to write a code doing the function as below:

(if (_the major mode is something_)
    (some function)
    (another funcion))

But I don't know how to write down the condition. 

Any suggestions. Thank you all in advance.

---

Teng