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.
From the timeline, open the visualization 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 swipe until you find it or search in search bar on top.
To see all items open "Search" tab on the bottom, and select "Items" on top.
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.
To easily access your favorite items, open an item and press the heart button in the top right corner. Now the item will be added to the top of your favorite item list and will show on your home screen.
On iPhone you can add your favorite items as a widget