No problem! You happened to catch me just as I loaded up my game.
Anyways, when you're in a sim's inventory, there is a box on the left with a simoleon sign in the middle. Clicking-and-dragging an item to that box will sell it. As shown:
A tip I didn't learn until much later was about multiple items, if you have a lot of one type of wildflower, for instance. You still click-and-drag, but to sell all of them at once, you click the corner of the item's picture and drag so all of the items in that stack will be sold: