An artist seal (落款) is pressed to finish a piece of calligraphy or painting. The word is short for «completed and inscribed» — it marks the work as done and stands in for a signature.
Shape
A tall rectangle is the usual form. Characters are carved top to bottom, moving right to left when there are several columns. Unlike business seals, the border is often thin or absent altogether.
Relief or intaglio
Artist seals lean heavily on intaglio: a red ground with white characters, which sits with real weight on the work. Carving the name seal in intaglio and the style-name seal in relief, then pressing them one above the other, is a long-standing convention.
Colour
Traditional seal paste is vermilion, chosen to sit against the black of ink. That is what the «Vermilion» preset is set to.
Where to press it
Usually at the lower left, below or beside the signature. There is no fixed rule — the position answers to the balance of the work — but it belongs in empty space, never over the brushwork.