First of all you need to have a account in http://box.net , login to your account.

Now follow 3 easy steps :)

Step1: Go to https://app.box.com/developers/services/edit/

boxdotnetappcreate-step1

Step2:  If step 1 is completed then , Click for configure
boxdotnetappcreate-step2
Step3: Copy client id and paste in plugin setting

boxdotnetappcreate-step3

Here is a practical usages of this application in one of our joomla extension “Box.net File picker for joomla

boxdotnetappcreate-step4