Make sure the gas supply is on
Open the oven door
Set the oven to the desired temperature
Locate the oven igniter or pilot light
If using a pilot light, light it with a long lighter or match
If using an igniter, turn the oven knob to ignite or bake
Hold the knob in if required until the flame stays lit
Check that the burner flame is on
Close the oven door
Wait for the oven to preheat