Its usually connected under the sink. The easy option is if you alreay have a 'T' piece under your sink with a blanking cap that you can unscrew and stick your waste pipe from the dishwasher to.
If you dont have a T connector fitted then you can buy one from most DIY shops. They're easy to fit, its just a case of unscrewing the old section and putting in the new one.
You may be better going to a plumbing merchants and explaining what you want as they'll be able to suggest the right part and give good advice.
Its not difficult to do. I'm useless at DIY and got mine sorted!