Yes, you can use either PG or VG (or a combination of both). PG will add throat hit but isn't good on vapor production. VG is great at producing vapor but has no throat hit, and it adds a bit of sweetness to your mix, which some like and some don't.
Using "Knoton's Mixing Helper" (thanks Knoton!), just enter 36mg in the box where it asks for "Nicotinebase", then enter your desired nicotine level (what you want to end up with) in the box for "Nicotine Strength". And lastly, enter the amount of eliquid you want to make (e.g. 5ml) in the box for "Amount". Leave the "2nd Diluent" and "Flavor" boxes blank (or enter 0) for now. If you know the amount of drops per ml that your dropper will provide, you can enter it in the box for "Drops per ml", or just leave it at 20 if you don't know.
Now on the right you'll see how much of your 36mg eliquid to use, and how much of diluent (PG, VG, or a mix of both) to use in order for you to end up with the nic strength you've told the calculator you want to end up with.
If you do decide to add flavor back in, just enter the percent of flavor you want to add to the final mix in the "Flavour" box and you'll see it reduce the "Diluent" quantity on the right by the same quantity of flavor that it adds, thus keeping the nic strength of your final mix at the level you're looking for.