If you're learning Cantonese you may very well want to get an overview of the language, some of its unique features, geographical information about native speakers as well as loads of information on grammar, linguistics, history, diaspora and general language structure.
All of this and more is available in Wikipedia's Cantonese entry. There are also some interesting links at the bottom which take you to further resources to explore and learn about the language of the Canton.
This may seem pretty obvious, but many people overlook reading the Wikipedia entry! Plus, most don't know about the related and useful Wikipedia category for the Cantonese language, which takes you much deeper into the language.