That is not an nginx configuration file. It is part of an nginx configuration file.
The nginx configuration file (usually called nginx.conf) will look like:
events {
...
}
http {
...
server {
...
}
}
The server block is enclosed within an http block.
Often the configuration is distributed across multiple files, by using the include directives to pull in additional fragments (for example from the sites-enabled directory).
Use sudo nginx -t to test the complete configuration file, which starts at nginx.conf and pulls in additional fragments using the include directive. See this document for more.