Hi @Preeti2,
A warm welcome to the Bunnings Workshop community and thank you for your question.
You'll have to start by preparing the soil. If you currently have weeds or existing grass, they should be removed before adding a layer of topsoil approximately 100mm thick and then levelling with a soil spreader.
Once the soil is prepared, you can either lay rolls of established turf or grow your lawn from seed. Turf rolls will be much easier and are likely the better option. You can order them through your local store's Special Orders desk and have them delivered straight to your door.
You can then follow How To Lay Turf for guidance on the installation of your turf.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
