You can select items using mouse or keyboard. If you prefer mouse, you need to press (and hold) the left mouse button. It defines the first corner of the area with selected items (the opposite one is dragged by the mouse pointer). While dragging you can move the mouse pointer near the edge of the view for scrolling the view.
If you prefer keyboard, you need to focus the first item, press (and hold) Shift key, it defines the first corner of the area with selected items, and then (the Shift key is still pressed) use arrow keys, Home, End, Page Up, and Page Down keys to move the opposite corner of the area.