If you’re troubleshooting the burner assembly on a gas dryer, one of the basic things ya just gotta know is the main parts: what they are and where they’re located. This photo shows the main parts of a gas dryer, click it to see the annotations of the various parts:

(click to enlarge and see annotation numbers)

1. Radiant Sensor
2. Ignitor
3. Flame comes out here
4. Flame Tube
5. Valve Coils (2)
6. For propane fuel, this will be a blocking pin; for nat. gas, this will just be a cap.
7. Gas supply pipe