Re: What’s integration?
You should certainly understand the integration process before installing as there are several key things you have to do differently – your config.php configuration will be very different, for example. If you have already installed bbPress then I think you will have to get rid of it and install it again, but integrating this time.
If you need help at any specific part of the process, feel free to ask here.
Also in mathematics integration is the opposite of differentiation.