Looking for basic information to learn to make ex4 files

I've done some googling for this and also searched this forum, but have not found the answer .. just pieces I am trying to put together.

How do you make ex4 files?
From what I can piece together, you first write a mq4 file, then use something to compile it into ex4. To modify it you modify the mq4 file then re-compile.
Is this correct? What is used to compile it? A separate program you have to buy or download or something built into MT4?
Why do some indicators come in pairs, a mq4 version and a ex4 version. What is the difference?
Is an EA coded differently than a ex4 file
And .. can anyone suggest a book or website where I can learn more?
I can modify mq4 code that is already written and I enjoy working with code so would like to learn how to do it myself from scratch, but I'm having a problem finding the basic info.
Thanks in advance

Check the link in my sig.

To compile an mq4 file you simply right click and choose 'compile' or hit F5 within MetaEditor.

Good luck

Lux

Thanks