There are two ways of accessing items; Either by opening the items view and select the item you want to explore or by selecting an item in a timeline.
Accessing items is currently only available on iPhone
From the timeline, open the visualisation options, select the item you want and press the "Open Item Info" button.
From the items list, select the item you want to explore by either swip until you find it or search in searchbar on top.
You can create a new timeline from the item by pressing the "Open in new timeline" button.
In the item view you can research your item, find values in a timeline and select a period to get the values from that period. Selecting a period is only an option for line charts, not status timelines.