how can identify two group of variable form some separate variables?

Hello every one.
I have five category of dairy products like milk, cheese,,, from one brand. The level of purchasing is define as a ordered value (very low, low,...,very high). It seems some categories have a same purchasing pattern. In fact I want to separate these 5 product into two or three groups. But I don't know the method.
Sorry for my poor knowledge!
Any help will be appreciated.