multi-line multi-pick fields?

multi-line multi-pick fields?

I am new to Zoho CRM, having spent the previous 15+ years with ACT. We have an agricultural irrigation company that deals with a lot of repeat customers. I would like to create a field in Contacts, that would let me categorize customers by the type of general products that they buy from us. For example, we have 8 major product categories, one customer may only buy in one category, but another may buy out of 4 or 5 of the categories. I would like a field that would allow my users to choose from 1 to 8 of predetermined categories. I have figured out how to make a multi-pick field, but I don't know how to let the user populate it with more than one selection. Thanks