How do I know which products to buy if I’m DIY?

How do I know which products to buy if I’m DIY?

To start you can look at the following which are good material to help. 
Sealing doors which is where most draughts come from can be a cheap place to start, refer https://ecomasterstore.com.au/pages/start-here-main

Here are some other products:

Sealant - Use a caulking gun to apply sealant for: 
skirting boards and architraves 
cracks in walls 
window frames 
general gaps. 
Always read the manufacturer’s label, wear gloves and, if necessary, use eye protection.

Gap filler rod - Use gap filler rod for:
skirting boards
large gaps
vents.
Gap filler rod comes in a range of thicknesses for different sized gaps or vents.

Expanding Foam - Use expanding foam for:
large gaps
hollows
cavities (for example, around fireplaces).
This can be messy to apply so be careful. Always read the manufacturer’s label, wear gloves and, if necessary, use eye protection.

Evaporative Cooler Vents:
Cover vents with either contact paper or specially designed magnetised vent covers over the cooler months to avoid heat loss 
Seal around the vent to prevent draughts.