How to get start with my first Redfish Schema

This really is going to depend on what your intent is. If you need to create OEM-defined resources that are not covered by the DMTF, then yes, you should follow that guide for crafting CSDL files. The JSON file produced in step 2 is not the same as the JSON file the interface emulator uses; the CSDL to JSON tool creates JSON Schema files, whereas the interface emulator uses JSON objects that represent payloads.

However, some of your comments make me think you might be trying to take existing schema files and use them in your implementation. If this is the case, you do not need to follow the DSP2055 guide, or do any sort of schema conversions. You can simply reference (or download copies of) the published DMTF schemas and use them as-is.

As a note about our versioning, many users have the expectation that the standard supports errata publications going back to the very first schema publication. That in turn creates many JSON Schema files. As an implementer, you do not need to support all of those versions; if you have a particular version of the Chassis resource you need to support, you just need that one JSON Schema file that represents that version. Having them all won't do any harm though, but it's certainly unnecessary.