Means its been pressed 3 times. And it has failed to ignite 3 times.
Its in a lock out state.
To prevent a bad ignition from doing damage to a tech or your house.
To test everything right. You need some tools, one of which would be an insulated screw driver.
So that you don't get hit with between 10,000, and 14,000 volts, from the ignition transformer.
Then you will need a part or 2 to check some other things, to see if they are bad.
Such as nozzle, oil pump strainer, oil filter cartridge.
Unless you happen to have a pump manifold kit.
So you might find it better to call a service tech.
Or, you should go out and get these parts before proceeding further.