But I still a bit confused about the request structure, and how to acquire them?
To find out how to make a request to an OGC web service (OWS), the best place to start is the standards documentation, for example for WCS, the documents listed at:
OGC Web Coverage Service standards
for example, how to find out which version to use, how to find out the coverage name etc)
The standard way to find out information about any OGC web service (CSW, SOS, WCS, WFS, WMS, WPS) is to issue a GetCapabilities request. A GetCapabilities request may include a version or version can be omitted (in which case you get a response from the highest version of the standard supported by the service). The general format (without version) is:
service-endpoint? service=[type of service] request=[type of request]
So in this case you could have:
or you could request versions as a list (latest versions of the OWS standards)
or request specific version...
The response gives you information on the names/identifiers of the coverages, the operations supported by the service, the extents of the data, the Coordinate reference systems you can request data in, the versions of the standard supported by the service, data formats, etc.
The version of the standard you use in subsequent requests will depend on the software you are using and what it can support, if the client can support multiple versions you should get a choice as a user as to which you would like to use or if, for example WCS with QGIS, only one version of the standard is supported then the client will use that version (QGIS uses WCS 1.0.0).
To find out more information about any coverage (without actually retrieving any data) you would use a DescribeCoverage request, like:
Note GetCapabilities is the only request type where the version parameter can be omitted.
And to get the data you issue a GetCoverage request.