Once signed into Acquire, select the Menu, or 'hamburger' button that looks like this:
Add a item by hitting the 'plus' icon (#2)
You will now be able to add item information here. (Asterisk-*- is required information). Once this is done, you can select the 'save' icon on the top right.
You can also add a picture of the item for easy reference as well. To add an image saved from the device's memory, select the 'Open Gallery' button, which will allow you to add this.
Once completed, you can select the 'save' icon at the top right, and the item will now be visible in the Pricebook.