You will be presented with the following screen. Go to Setup.
Now, Go to Platform Tools -> Apps -> App Manager.
Click on New Connected App.
You will be taken to the application settings page. Configure the application like so.
Check the Enable Oauth Settings and you will be shown more options to configure, Such as, Callback URL (Enter from miniOrange Oauth Client plugin which you copied in the last step) and Scopes. Select the scopes as required. Make sure that the same scopes are also added in miniOrange Oauth Client plugin and then scroll all the way to the bottom to click on Save.
You will be taken to Application Management page. Here, you will find Consumer ID and Consumer Secret.
Copy these credentials and keep it handy because you will need it in the next step.
You have successfully completed your Salesforce App OAuth Server side configurations.