Drag tasks between sprints, drag a marquee to select several at once, and Shift+click to add tasks to your selection.
Selecting tasks
- Click a task once to select it, replacing whatever was previously selected.
- Shift+click another task to add it to your current selection.
- Click and drag on empty canvas space (not on a card) to draw a marquee box — every task inside it is selected when you release.

Moving tasks between sprints
Drag a selected task (or a group of selected tasks) onto a different sprint column to move it there. Dropping it re-parents the task into whichever sprint's area it lands in.
What to do about it
Build a selection with Shift+click or a marquee before dragging if you want to move several tasks together in one action, rather than dragging them one at a time. There's currently no Ctrl/Cmd+click shortcut for selection — Shift+click is the only way to add a task to an existing selection.