A DTG printer works like an oversized inkjet. The garment is loaded on a platen, the printer lays down process inks (usually CMYK), plus a white layer on dark or colored garments, and the print is heat cured with a press or dryer. Because the image is digital, a full-color photo costs no more to set up than a one-color logo, and every shirt can carry a different design.
DTG performs best on cotton and cotton-rich blends. On darks the garment needs pretreatment so the white ink stays up on the fibers. On light shirts the print is softer than most screen printing; over a white layer it is a little firmer. Exact Pantone matches and metallics are beyond its reach, and only a few high-end systems carry fluorescent inks.
It suits small runs, one-offs, samples, many designs in small quantities and print-on-demand. For large runs of simple designs, screen printing usually costs less per piece. Compare them in screen printing vs DTG and DTF vs DTG.