$sudo apt-get install apache2
$Sudo apt-get install nginx
Both installed but only apache is running and if we go for nginx after stopping service of apache ,nginx service is running but not showing its default page!! Please help to resolve
You can't listen to same port with two servers but if you want you can configure Nginx as a reverse proxy for apache. Here is a great tutorial to do that https://www.digitalocean.com/community/tutorials/how-to-configure-nginx-as-a-reverse-proxy-for-apache. You can also check this one http://kbeezie.com/apache-with-nginx/ .
Hope this might help you.
As it has already been stated above, it is impossible to run different services on the same port as only one service can run on a port at a time. You can however run Nginx as a proxy server (each one running on a different port).
Note: you can configure each server's document root to load different home pages when both are running on different port (if that is what you want).