The easiest way to enter items on your list is to swipe suggestions shown on the red suggestions screen. Swipe with 2 fingers to the right to see it. In the first month, commonly bought items (in your language) is shown here. After that, suggestions based on your actual shoppings habits are shown here.
Another easy way to add items is by right-swiping them on the green history screen for a previous shopping trip. Swipe with 2 fingers to the left to see it – tap the divider bar for each trip to open up the trip in question. This will copy the item onto your current shopping list.
You may also dictate item names using the dictation button on your phone keyboard.
And of course, you may also just enter the grocery using text input field at the top of the shopping list. It has predictive auto complete function that looks at your purchase history and shows the most relevant items related to the typed characters.