Using Zoho CRM in a Cloth Store

Using Zoho CRM in a Cloth Store

I have a cloth Store here in Brazil and I`d like to use Zoho as a CRM and to control my inventory.
I don`t really need Leads and potentials, I just need a list with all my clients and the purchase history.
How can I implement it? Do I use the Leads tab to save my clients? Or the contacts tab? How can I subtract an item from the inventory?

Its simple, but I wasn`t able to do it..

Thanks!