Drag across a line to warp it. Hold Alt while dragging to invert the effect (Expand becomes Pinch, Push reverses direction, Twirl reverses spin).

Click empty space on your drawing to place a pin, then drag a pin to pose it -- move the timeline first to pose it differently at a new moment, each pose you drag becomes a key there. Click a pin to select it, then press Delete to remove it (or Alt+click it). "Show pins" only hides the pin markers visually, it doesn't affect posing. Right-click a keyframe on the timeline for the option to delete just that one.

Record: drag a pin to capture its whole motion live, instead of one pose at a time -- the timeline plays automatically from the start of its loop range while you drag, and every moment of that motion is baked in when you let go or it reaches the end. A recorded pin locks in place until Record is turned back off.

Drag outside the selection to draw a new one. You'll see it highlighted as you go. Hold Shift while dragging to add a new area to the selection, or Alt to subtract an area from it (or use the New/Add/Subtract buttons above). Once selected, drawing is confined to inside it, a click inside fills it with the current color, Delete/Backspace erases everything drawn inside it, and dragging inside carries the drawing along with the selection.

Click anywhere to flood-fill the connected area under the cursor with the current color. If a selection is active (from the Lasso tool), the fill stays confined inside it.