Cannot create a database connection SQL Developer I will try to explain the current situation in the best possible way.

Well, I got a VM with SQL Developer already installed but could not run properly. After some reasearch, I solve the problem related with environment variables.

Currently, I need to create a database connection but unsuccessfully. I do not know what are the credentials that I have to use it. I can log in on sqlplus as sysdba. 

I already did the select * from all_users but I am still stuck on this. Is there anyway to discover the right credentials to create the connection?

Thanks anyway.
I was putting the wrong service name. You can check yours on tnsnames.ora.