When I shoot I start with an image that is fairly flat for grading
in post but I'm not sure which of the PP to use. I've been using PP6
which looks flatter than the rest. Also can someone explain to me
what detail is? I think it's sharpness but I didn't notice any difference
while changing the levels .I've been using a Canon 7D for the past two years
so PP are new to me I'm trying to learn what each setting does and which are
the most important ones to tweak.

Picture Profile 6 is quite a good starting point.

You might want to look through this:
Picture Profile Guide. | (http://www.xdcam-user.com/picture-profile-guide/)

thanks Alister I'll have a look at the link.