Thanks to @a_5mith and @Peter-Zoltan-Keresztes

here is the nginx.conf
user www-data;
worker_processes 1;
pid /run/nginx.pid;

events {
worker_connections 768;
# multi_accept on;
}

http {

##
# Basic Settings
##

sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 65;
types_hash_max_size 2048;
# server_tokens off;

# server_names_hash_bucket_size 64;
# server_name_in_redirect off;

include /etc/nginx/mime.types;
default_type application/octet-stream;

##
# Logging Settings
##

access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;

##
# Gzip Settings
##

gzip on;
gzip_disable "msie6";

# gzip_vary on;
# gzip_proxied any;
# gzip_comp_level 6;
# gzip_buffers 16 8k;
# gzip_http_version 1.1;
# gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

##
# Virtual Host Configs
##

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;

}

#mail {

# See sample authentication script at:

# http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript

# auth_http localhost/auth.php;

# pop3_capabilities "TOP" "USER";

# imap_capabilities "IMAP4rev1" "UIDPLUS";

server {

listen localhost:110;

protocol pop3;

proxy on;

}

server {

listen localhost:143;

protocol imap;

proxy on;

}

#}

@a_5mith
Did that but not working

I have installed nodebb but can't use domain.com instead of domain.com:4567.Can anyone please help.When i installed installed node bb i used explorehowto.com as base url
This is my config.json
{
"base_url": "http://explorehowto.com",
"port": "4567",
"secret": 'xxxxxxxxx",
"bind_address": "0.0.0.0",
"database": "redis",
"redis": {
"host": "127.0.0.1",
"port": "6379",
"password": "",
"database": "0"
},
"bcrypt_rounds": 12,
"upload_path": "/public/uploads",
"use_port": false,
"relative_path": ""
}

This is what i have inserted in
cd /etc/nginx/sites-available/
sudo nano explorehowto.com

server {
listen 80;

server_name explorehowto.com;

location / {
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_set_header X-NginX-Proxy true;

    proxy_pass http://127.0.0.1:4567/;
    proxy_redirect off;

    # Socket.IO Support
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
}

}

But it doesn't run on explorehowto.com but instead running on explorehowto.com:4567

@a_5mith
is this right
git clone -b v0.5.x https://github.com/designcreateplay/NodeBB.git .

Don't mind installed again.
But whenever i am installing it is installing development version and not stable.How to solve it

i have disabled last 5 activated plugins.But still error shows up.
Does my ./nodebb setup is correct what i have above stated

I have installed nodebb and configured correctly.It works for 20 min and then if i installed any plugin or theme it is showing the following error occurs saying"502 badgateway"
These are my configuration
url accessed to use nodebb"http://explorehowto.com:4567"

then in
cd /etc/nginx/sites-available/
sudo nano explorehowto.com
i have inserted the following command
server {
listen 80;

server_name explorehowto.com;

location / {
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_set_header X-NginX-Proxy true;

    proxy_pass http://191.101.6.63:4567/;
    proxy_redirect off;

    # Socket.IO Support
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
}

}

server {
server_name www.explorehowto.com;
return 301 $scheme://explorehowto.com$request_uri;
}

I have sucessfully installed nodebb.how to change nodebb's category.
for
example:- domain.com/category
to
category.domain.com
I am not referring to external domain in the category.In simple words i want sub-domain forums.Is it possible

OK PROBLEM SOLVED