I've bought a new stove which is supposed to be auto ignition. If I turn on the gas and turn the knob thing, a flame flickers underneath but the stove doesn't light, I have to use a lighter to light it.
Any ideas what I'm doing wrong?
A couple of things. First, you just bought it, it surely came with a manual, you should check there to make sure you're doing it right.
In general there are a couple of things that come to mind:
What type of ignition switch is it? Some of these are run by a spark plug and/or a battery. Does yours have this? and have you checked to make sure those are firing correctly?
Even still you should be able to leave the gas off and look for a spark.
My experience with the modern home appliance gas stoves is that all the parts that constitute the heating area disassemble easily. This includes the burners.
When I've had problems with burners not lighting, it has always been:
Note: Am including information for both electronic (spark) ignition and pilot ignition stoves.
So, all that being said, your statement that "a flame flickers underneath but the stove doesn't light" leads me to the conclusion that the burner body(s) are slightly misaligned, allowing combustible gas to leak out at the bottom of the burner assembly - or, that the pilot light or spark electrode is misaligned.
Take one burner apart; if it is a simple matter of lifting the parts off (which it should be, as they do need to be cleaned and the spilled food dug out of the gas ports occasionally) and get to know how it fits together. If all is well there, check the ignition source for location in the proper place to ignite the combustion gas coming out of the burner in the proper place.