The screens below are used for three purposes. Vendors can be selected, and even be created "on the fly," to make purchasing easy. You also assign selling prices for each item at the time you purchase it (of course these can be adjusted later). Finally, you conduct the actual purchasing process from the menu and its accompanying screens.
UPDATED PICTURE HERE
The menu you see above will be "customized" for the industry you select on setup. For most industries, you can select 1) to get started. The screen below will then be presented.
UPDATED PICTURE HERE