How do you test an app on a real device with xCode?

Hi :) firstly you have to be registered as a developer, not the same as enrolle in the paid developer program. You just need your Apple ID to register as a free developer and you can run 3 apps per device freely.
Then in Xcode you have to go to preferences and add your Apple ID in the accounts tab.
Then the project has to be as part of your team, which means associated to your account in Xcode basically.
The easiest way is to configure it when you create the project, although it is possible to do it in an existing project.
You just go to the project navigator (sorry if I am mistaking the terms with Eclipse's, currently I'm not on my personal computer where I use Xcode), the one you access with cmd+1, go to the root of your project and then you have to navigate the editor pain until you find the signing & capabilities editor and then you associate it with your team.

I've done a step by step explanation in the blind programmers mailing list, I will try to find it and paste it here to see if it helps more than this hurried explanation during a coffee break

I am changing jobs and yesterday was a very busy day, I didn't have time to come back to the topic.

I found today my step by step instructions that I sent before in the Visually impaired programmers mailing list, I think they are still up to date and I hope they can help! But don't worry, from now on when you create a new project and associate it with your team, it will be much easier. Nonetheless it is good to know how to navigate the project properties screens.

Firstly go to the project navigator and choose/focus on the top most element of the project.
Then on the editor view go to the {YourProject}.xcodeproj group.
Then go to the third group, called project editor tab chooser radio group and interact with it. Select the second radio button: Signing & Capabilities.

Then, interact with the element after the project editor tab chooser, called project editor split view split group.
Navigate until the seventh element, a scroll area, and interact with it.
Then interact with the element Signing expanded disclosure group, that reflects the element activated in the project editor tab chooser in the second step.

Then after passing some elements you will find the Team label and then the Team Selection Pop Up Button. Here, if you already added it, you can select your account.

Great, configuring when starting a new project is the fastest way!
There are lots of configurations to do in the project settings, when you need to use them you already know where to find them.

Have fun developing and testing ;)

Just to clear things up, you don't need to be a developer to test on your own device. Only oif you want to distribute the app you need to be registered as an Apple Developer and pay the $99 fee.