One of the ways that QuickBooks simplifies your life as your company's accounting manager is by providing pre-designed record and form templates. Need to create an invoice? There's a form that already contains the most commonly-used data fields; you just fill in the blanks or select from drop-down lists. Want to store information about your customers and about the items you sell? Ditto.
But if you need more fields than QuickBooks offers on a record or form, you can easily add your own. The software lets you add 15 fields total to customers and jobs, vendors, and employees, and you're limited to seven for any one record type. (If you want to use the same field in two of these, it will only count as one.) And you're allowed to define up to five fields for your item records.
This type of modification is easy to do, but it's critical that you think carefully about what fields you should add. You don't want to learn three or six months down the road that one isn't really necessary and two more are needed, for example. This is especially important when you're creating records for inventory items.
You may want to schedule some time with us to go over this (and to explore QuickBooks' item-tracking features if you're new to managing inventory). You can change custom field names, but you need to understand how this will affect your data if you do this.