How to create two distinct portfolio pages with separate content

Hi,

My site is http://www.edward-hall.co.uk

I have a showroom page, which uses portfolios to link to the individual pages of each car. I would like to create a second, similar page (entitled Part Exchanges, Projects & Parts) that’s set up in a very similar manner.
I have tried to do this but cannot find a way to ensure that the project car portfolios stay on their page and the showroom portfolios stay on theirs, they are duplicated across both pages. I realise you can create more than one portfolio but they remain accessible under both pages and, in any case, I would rather completely separate them on different pages.

I have searched for this topic and found people in similar situations, however none seemed to answer in a comprehensible way.
I must point out that I DO NOT understand code, coding or anything like this. Whilst I did not put together my website I administer it and change it and I have managed to figure my way through most problems, but not this one.

I would be very appreciative if someone could explain how to do this is the simplest of terms.
Many thanks for your help in advance.

Edward