There are two ways to carve a seal, and they differ in which part gets cut away.
Relief (陽刻)
The characters stand proud, so the characters print red and the background stays empty. Most seals you see work this way, and the legibility suits business documents.
Intaglio (陰刻)
The characters are cut away instead, so the ground prints red and the characters stay white. The result is heavier and denser. Artist seals pressed onto calligraphy and paintings are traditionally intaglio.
Often used as a pair
In East Asian painting it is an old convention to press an intaglio name seal and a relief style-name seal one above the other, so the two balance each other.
In BaroStamp
Switch between them under Carving. Intaglio fills the body of the seal with colour and cuts the characters completely transparent, so the paper beneath shows through the strokes exactly as a real impression would.