I am wondering where can I find some steps to create a staging for EE2 ?
If you know how to create a production or development server for EE2, you can create a staging server... if you don't know how to create a development or production server then go find that out first.
There is no elegant fix for this - how you solve it very much depends on what you use the CMS for and what sort of changes you plan on making.
This is not an EE issue specifically - you'd have the exact same issue with any database driven CMS.
If you give some more info on what kind of environment you want the staging server for, maybe there is scope for a more complete answer, but for the generic concept this is it.
You might want to consider this Bootstrap file from Ben Parizek (originally from Leevi Graham). It allows for Local, Development (Staging) and Production (Live) environments. You can set different environment variables and database connections for each. Works well if you're using (and you should be) a code versioning system, and the some kind of deployment tool.