Now and then, in business and sometimes other matters, you are requested to sign a Non Disclosure Agreement (NDA).
My advice is to unchanged, refuse to sign them unless you have too.
Some companies will email you an NDA first and tell you in that email that the discussion is bound by this NDA, the legality or enforceability of this I do not know.
However, sometimes you must sign it, and sometimes it is fair and reasonable that you do sign it. In most cases, there's nothing wrong with signing the offered NDA. It is likely not personal as many consider it a regular part of doing business, a sign of good faith.
Sometimes you need them too!
If for example, you get a great idea in business and want to discuss it with a supplier of yours. You do not want them to spread it around, but you do want to talk to them about it, well that is what an NDA is designed to do. Another example might be that you have a client list, a company is going to do some marketing that should be useful for you but you do want your client list kept confidential so again an NDA can be useful.
Some companies insist that their employees sign it if you work for the US President you need to sign three NDAs.
Do they work and how much validity do they have, I am not sure but I think you are often better off with one than without one.
Having decided that you would like someone to sign it first and they agree to sign it then how do you get one? You probably do not want to spend money with a lawyer.
This is a problem I faced a short time ago.
So I did a net search and discovered an Australian government site which supplies NDAs free here.
Fill in the form, and it creates an NDA for you, which you can edit. It appears to be fair and reasonable. You may consider using this.
Note: I am not a lawyer, I do not pretend to be one, and you would be well advised to discuss this matter with a lawyer.