Bundle ID is a unique identifier that allows Apple to uniquely identify your application among all others. It is used for the following purposes:
In order to change a bundle ID of an already existing application, select it in the project navigator, click on General present in the top menu, and if needed, open the disclosure triangle near Identity. There you will have the bundle ID as shown in the following screenshot. The usual format for the bundle ID is
com.<company>.<project>, and this helps to keep your ID unique.