You will need to open/remove the lower front panel of the dryer and observe what occurs

Start the dryer on a heating cycle,
you should hear a click, then the igniter should start to glow red. After a few seconds of glowing, you should hear another click, the igniter should start to fade and the gas should ignite,and have a flame.
Indications,
No click at start, possible thermostat or power supply problem to or at the gas valve.
Click,but no glow, bad igniter or flame sensor switch.
Click, glow but no fade, bad flame sensor.
Click ,glow, fade, but no flame, bad gas valve coils.
These are the more common problems for your complaint, but there are others.
Let us know what you find and we can go from there.

Thanks,
:) :) :)