Well, since you ordered it from Public Missiles I assume you read or have the ability to go back and read the full page description they have on their website (hint: they also link to pdf sheet of specific instructions on how to use their foam, which probably will also be included with your foam when it arrives). PML sells a kind of two-part foam with variable expansion rates, from 10 up to 25 times its liquid volume. So.....
1) Figure out what expansion rate you want, more or less dense foam? Why are you foaming this nosecone, are you just using it to lock in some noseweight? Less dense should be fine.
2) Figure out the volume of your nosecone. You can approximate, just treat it as a cylinder instead of a cone, this will make sure you have plenty. (Interpolate and knock off 20% if you want to be economical or have less cleanup.) Use google to figure out the equation for the volume of a cylinder. Use a calculator to figure out the equation.
3) Use your answers from 1 and 2 and some more math to figure out how much of Parts A and B you want to mix.
4) Also don't be afraid to use the search function here to browse through earlier threads on "two-part foam" for additional tips, I'm pretty sure you will find some. Drill a big hole, too small and it will be harder to pour in. You don't need a funnel, just mix in a disposable cup and pour. Having a bucket of cold water ready in case it starts to get too hot isn't a bad idea.