how do you use Lr mobile on your desktop?

Lightroom Desktop is the Cloud Based equivalent of Lightroom Mobile, with all photos and edits syncing across both.

You would require a Photography Plan to use it (you may already have one). The Cloud only Plan is approx $10US/£10 for 1TB Storage.

If you just have the Mobile Plan then you may be able to access your Library at Photo Editor | Online Photoshop Lightroom where you cam do most edits but doesn’t have all the functionally of Lightroom Desktop.

Mobile is for iphone and/or android

Minimum System requirements for Cloud Programs... scroll down and check each program

-http://helpx.adobe.com/creative-cloud/system-requirements.html