You can add new items to your collection in a number of different ways. Here's the breakdown:
In list view, just click on the "Add Item..." bar at the top and start typing.
When working from a mobile device a big, round "+"-symbol in the bottom right corner appears with which you can add items to the view.
In Kanban view, click on the "+" button next to the list name to create a new item at the top of that kanban list.
Or you can hover over the bottom of a list you’d like to add an item to and the "Add Item…" button will appear.
In calendar view in month mode, hover over the date, then click the "+" button in the top right corner. In case you are working with a mobile device, the "+" icon is in the top right corner of the collection. You will have to add the date manually.
In calendar view in week mode, hover over the date and click the "+" button in the top right corner.
In table view, each row represents one item. Click on the "+" icon in the top left corner to create a new row.
You can also click anywhere in the grey bar that appears at the bottom of the table and starts typing. In any view, hit 'Enter’ after you’ve added an item to add the next one. Just as calendar view you will see a small "+" icon in the top right corner of your mobile version to add items.