Xcode error: Code signing is required for product type 'Application' in SDK 'iOS 10.0'

To add developer account to Xcode:

1. Press Cmd ⌘ + , (comma)

2. Go to Accounts tab

3. Follow the screen shot below to enable development team:

With Xcode-8.1 & iOS-10.1

1. Add your Apple ID in Xcode Preferences > Accounts > Add Apple ID:

2. Enable signing to Automatically && Select Team that you have created before:

3. Change the Bundle Identifier:

4. Code Signing to iOS Developer:

5. Provision profile to Automatic:

You can now run your project on a device!

In case you are still having this problem, click on the Tests and select a team for them too.