Good day, zwenigroup6.

In the mobile version of QuickBooks Online, you can add a regular product or service item. 

Here's how:

1. Click the Hamburger (indicated by 3 horizontal lines) icon.
2. Tap the Products & Services box.
3. Select the + icon and add the new product or service details.
4. Tap Save.

To add a stock item, you'll want to log in to your QuickBooks Online account using the web browser. I've got this article for the instructions: Add stock products in QuickBooks Online.

I'm just a few clicks away if you need anything else. Take care.