If you do not care about best practices, you can take a look at nginx.conf and see which directory is included. It will probably be nginx/conf.d/*.conf, so you can store your configs there and they will work after restarting (or reloading) the nginx service.
However I will try to answer simply with the standard nginx approach, regardless of the distro:
nginx comes with the nginx.conf file inside /etc/nginx. There you have a block, which tells nginx to read additional .conf files from the directory conf.d.
*.conf-Files inside /etc/ngninx/conf.d
This is the default directory, which nginx creates after installation. It is used to store virtual host configurations in the *.conf format. However, this is not the best approach.
*.conf-Files inside /etc/nginx/sites-available
A more elegant approach is to have the .conf file of your virtual host situated in sites-available.
*.conf-Files inside /etc/nginx/sites-enabled
This is where you would symlink the virtual hosts from sites-available, to make nginx read and work with them.
For this approach to work, you would need to edit nginx.conf and have it serve conf files from sites-enabled.
After that, in order to add a new vhost to nginx, just create a symlink.
ln -s /etc/nginx/sites-available/mycoolsite.conf /etc/nginx/sites-enabled/mycoolsite.conf
Restart nginx and you're all done. mycoolsite will now be served by nginx
service nginx restart
