Proper contract template/guide to share?

All the while I have using email conversation by asking for client’s real name and all other details prior running the work.
Lately I have been wondering what is actually the proper way of doing contract? Is there good NDA type of contract guide to share?

Searching on Google gives me all those contract guide which actually involves in face-to-face type of contract meeting that use PHYSICAL PAPER to sign. I have never once signed any contract neither the other side did. Do I really have to sign something on email? I am usually working online. I am asking to clarify further as I am ignorant here.