Install the SDK on a desktop system and read the documentation, including the examples.
The SDK is for the use of a programmer who understands REST/CRUD/SOAP -- the documentation is fairly clear on what it does.
I would advise installing it on a workstation and running any program you write against a development/test instance.
v2/v3: there are some verbs that only work on v3.
yes it can query the NPM database (examples included in the SDK)
the programs that use the SDK can tun anywhere with a network connection, on any platform, that can reach the Orion server. I run my [perl] programs on a RHEL linux system. If you've a powershell programmer, java programmer then they could get their programs to work on their platform of preference.