Server blocks are the actual configuration pieces that tell the server what to serve and on which port to listen. We can define multiple server blocks in the sites-available folder. On Ubuntu, the location will be as follows:
/etc/nginx/sites-available
On Mac OS X, the location will be as follows:
/usr/local/etc/nginx/sites-available
Until we create a symlink from the sites-available to the sites-enabled directory, the configuration has no effect. So, always create a symlink for sites-available to sites-enabled for every new configuration you create.