This website describes the principle of the hue bridge and the app "all 4 hue", which is available for Android and iOS. Some functions of the app are only available in the Android version; this is mentioned at the corresponding points in the documentation.
You can either start from the beginning with the basics of jump with the menu directly to the section which is relevant for you.
In the last section of the website answers to frequently asked questions are given.
The website is also available in German.