There’s nothing wrong with practicing informal English from time to time, especially if you are aware of how language works in different contexts.
English tends to contract structures in order to economise language and promote fluency, and sometimes the way words are produced when put together gives birth to idiomatic expressions that may sound the very same in oral form but are spelt differently if you write them down.
In order to get acquainted with expressions like these, you can visit the following webpage and, after that, start using them with old and new friends from abroad.
Watcha gonna do ‘bout it?