The main features.

Paint behind your lines

Every layer holds a line sheet and a paint sheet. One key flips between them, so you can lay in tone under your lines without touching them.

1. Draw the lines. The Brush on the line sheet, with pressure on every stroke.
2. Press Q to flip to the paint sheet. The lines stay on top.
3. Paint tone with the Paint Brush. Paint over the lines as much as you like; it goes behind them and never touches a line.
4. Or let the bucket do it. The paint is cleared to show the faster way.
5. One tap of the paint bucket fills the whole figure, tucked under the lines. It closes small gaps in the line work, so the fill doesn't leak.
6. Touch up the last specks with the Paint Brush.

Onion skin

See the panels either side of the one you're drawing, in fixed colours: red before, green after.

1. A four-panel board, onion skin off.
2. Turn onion skin on with the button or O. The panels before show in red, the panels after in green, fading with distance.
3. Step through the panels and the ghosts follow, so you can check the action and the spacing.
4. Choose how many to show. Here After is set to 0, so only the panels before appear.

Also: layers with names, opacity and visibility, and reference images dropped in from Finder.