mjhjmtu

service nginx start
Redirecting to /bin/systemctl start nginx.service
Job for nginx.service failed. See 'systemctl status nginx.service' and 'journalctl -xn' for details.

[root@myvps ~]# systemctl status nginx.service
nginx.service - The nginx HTTP and reverse proxy server
 Loaded: loaded (/usr/lib/systemd/system/nginx.service; disabled)
 Active: failed (Result: exit-code) since Tue 2014-12-23 03:48:02 EST; 10s ago
 Process: 19895 ExecStart=/usr/sbin/nginx (code=exited, status=1/FAILURE)
 Process: 19892 ExecStartPre=/usr/sbin/nginx -t (code=exited, status=0/SUCCESS)

Dec 23 03:48:00 myvps nginx[19892]: nginx: configuration file /etc/nginx...ul
Dec 23 03:48:00 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 ...e)
Dec 23 03:48:00 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 ...e)
Dec 23 03:48:01 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 ...e)
Dec 23 03:48:01 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 ...e)
Dec 23 03:48:02 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 ...e)
Dec 23 03:48:02 myvps nginx[19895]: nginx: [emerg] still could not bind()
Dec 23 03:48:02 myvps systemd[1]: nginx.service: control process exited,...=1
Dec 23 03:48:02 myvps systemd[1]: Failed to start The nginx HTTP and rev...r.
Dec 23 03:48:02 myvps systemd[1]: Unit nginx.service entered failed state.
Hint: Some lines were ellipsized, use -l to show in full.

[root@myvps ~]# journalctl -xn
-- Logs begin at Mon 2014-12-22 15:26:47 EST, end at Tue 2014-12-23 03:48:02 EST
Dec 23 03:48:00 myvps nginx[19892]: nginx: configuration file /etc/nginx/ngin
Dec 23 03:48:00 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 faile
Dec 23 03:48:00 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 faile
Dec 23 03:48:01 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 faile
Dec 23 03:48:01 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 faile
Dec 23 03:48:02 myvps nginx[19895]: nginx: [emerg] bind() to 0.0.0.0:80 faile
Dec 23 03:48:02 myvps nginx[19895]: nginx: [emerg] still could not bind()
Dec 23 03:48:02 myvps systemd[1]: nginx.service: control process exited, code
Dec 23 03:48:02 myvps systemd[1]: Failed to start The nginx HTTP and reverse 
-- Subject: Unit nginx.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit nginx.service has failed.
-- 
-- The result is failed.
Dec 23 03:48:02 myvps systemd[1]: Unit nginx.service entered failed state.

and /lib/systemd/system/nginx-service

[Unit]
Description=The nginx HTTP and reverse proxy server
After=syslog.target network.target remote-fs.target nss-lookup.target

 [Service]
 Type=forking
 PIDFile=/run/nginx.pid
 ExecStartPre=/usr/sbin/nginx -t
 ExecStart=/usr/sbin/nginx
 ExecReload=/bin/kill -s HUP $MAINPID
 ExecStop=/bin/kill -s QUIT $MAINPID
 PrivateTmp=true

 [Install]
 WantedBy=multi-user.target

and

nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

and

netstat -tulpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name 
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 17005/mysqld 
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 769/sshd 
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 772/sendmail: accep 
tcp6 0 0 :::80 :::* LISTEN 1373/httpd 
tcp6 0 0 :::22 :::* LISTEN 769/sshd 

I installed nginx-1.6.2-4.el7.x86_64 on my centos 7 64 bit using Epel 7.5

As @masegaloeh says, you have another process listening on port 80, in this case httpd. You'll need to stop that service first (and probably want to disable it on boot).

To stop Apache;

systemctl stop httpd

To stop Apache starting on boot;

systemctl disable httpd

A port can't handle two services at same time.

systemctl stop httpd
systemctl disable httpd

Then

systemctl restart nginx