These OID are based on Windows SNMP OID, and can be used with Net-SNMP as well.
For those x value, you can use a MIB browser to get the appropriate value for your own device. Here I suggest to use this one: http://www.manageengine.com/products/mibbrowser-free-tool/
You can get the MIB file named HOST-RESOURCES-MIB.txt which contains all the information of the host online.
Processor usage percentage:
Storage Size (include Physical Memory, Virtual Memory, Storage Devices)