The DVA has lots of information on its NI Direct website about how to apply for your LGV provisional driving licence.
You can book the LGV theory test online here.
And there is a link to information on the practical driving test for lorry drivers here.
There are 6 centres in Northern Ireland where a Theory Test can be completed – for more details and direction, please go here.
If you have any special requirements or need additional help to complete the Theory Module there is more information on the options available for you here.