Use pbf2png -h for help. The parameters should be self-explanatory, except the -M - tile name mask parameter. It's only there because of the notoriously known design flaw in the Mapbox vector tiles specification - the missing zoom level in the tile data. To render a tile, a workaround that fetches the zoom level from the file name (or somewhere else) is required. The default mask(regular expression) is ([0-9]+).* which should fit all common tile name schemes like $z-$x-$y.pbf, $z_$y_$x.mvt, etc.

Styles

See the QtPBFImagePlugin documentation for how to set the style used for rendering the tiles. For the default OpenMapTiles data schema and the default OSM-Liberty style nothing needs to be done.