It is not possible to register a .net or .com domain name for free. If you want a free domain name, try out .tk or .cu.cc or .co.nr . There are many others available that you can register for free.
To be honest, I wouldn't recommend them if you are trying to register a domain for business or commercial purposes. If you are trying to reach out to an audience, they must be able to reach you. domain names that are registered for free reach out to minimal audience because of these extensions do not reach out to many. Even using the best SEO methods would still make it a problem bringing it up.
If you are registering for a personal domain, a free domain would be suitable for you.