where I can find the ides documentation for variant configuration?
Exactly what documentation are you talking about? There is very little documentation about IDES itself except the IDES installataion guide.
You can get a general idea of what is (and is not) available in an IDES installation by referring to OSS note https://service.sap.com/sap/support/notes/799639
I hope you are not expecting that SAP course training materials are part of IDES. Although SAP training is usually done on an IDES system, the course materials are part of the course, not IDES. To obtain a legal copy of these you must register for the course and pay the course fees. Review https://training.sap.com/us/en/search?query=Variant+configuration
There is some nice (free) Variant Configuration docs in Best Practices.
See this file and try to run the scenario as per this it will give you good understanding of Variant configuration.