When do you use the words after which?
Let me take my shower in the morning first because, after which, I need to get my errands done. That is an example of when you would use that phrase.
You can use any words you wish to use in a book. Most writers have characters who do use "bad" words - I am assuming you mean vulgar or curse words. The trick is, don't use them just to be using them! Make sure you have a good reason for including vulgar language, or nobody will want to read the book because it will just be a list of curse words.