Add Items to an Activity in the Item List section of the Author Site Activity Editor.
Once you have hit the + Create button in the top right of the Activity editor view you can begin to populate the Item list for the Activity.
Under the Items tab of the Activity editor, you can select Find items or + Create item. This allows the author to either select a previously created Item from the Item bank or create a new Item.
If the Find items button is selected, you will be brought to an Item bank page where you can search for the Item using the search fields. You can also preview an Item using the preview button to the left of the Item reference. Once the Item is found you can select it by checking the checkbox on the left of the Item in the list. You can add multiple Items at once. When you are happy with your selection, simply click Add items(s) at the top of the Item list.
Please note only published Items will appear in this view.
+ Create Item
It is also possible to create an Item for your Activity on the fly. Once you hit the + Create item button you will be brought to an empty Item upon which you can begin to add your content (Questions/Features). You can look at the documentation for Item authoring here.
Once you have created your Item and are happy with it, hit save in the top right corner and then hit Back to Activity edit in the top left corner where you can add additional Items to your Activity.
Items will appear by default in an assessment in the order you have added them to the Activity. To change the order of the Items appear in an assessment, click and drag the Item References around in the Activity Editor. You can add or remove Items from an Activity at any time.