best practice either create multiple databases or multiple users I have several application which currently running on my local. I have installed oracle 11g and create a global database name as oracle11. Now should i create again different database for each application using Database configuration assistance or should i create different users for each application under that global database? What would be the best practice? If i create different users its also behave same as creating different databases right?

What if in a production environment where server house for couple of application? Do i need to do the same as my local by creating one database and different users for each application?
Databases use server resources: CPU, RAM, disk I/O.  Unless your server is physically partitioned (e.g. Solaris Zones) or you are using VMs it is a really bad idea to host multiple databases on the same server.  You are just creating an environment where contention will be rife and tuning will be even trickier than normal. 

Oracle RDBMS has always been designed to host multiple schemas in the one database, and for different applications that is the way to go.  This is one of the main differences between Oracle and (say) MS SQL Server or MySQL.