1. Select one item by clicking on it.

You can then select more than one item by holding the SHIFT key or the CTRL key and clicking on another item.  

    2. The SHIFT key will select all the items in-between the first selected and the last selected.

    2. The CTRL key will add only this item to the selection.  If it was already selected, it will remove it from the selection.

    2. To select all items, you can do CTRL+A.

You can get a reminder of how to do this by clicking the Keyboard Shortcuts button at the bottom of the screen :

TIP: You can select a range of items with the SHIFT key (or all items with CTRL+A), then unselect only a few items by holding the CTRL key and clicking on the unwanted.