When you open a reply box, you can see a little gear icon in the far-right corner at the top of the screen. When you click on that, it’ll present you with four options: insert table, hide details, build poll, and blur spoiler. Obviously, you’ll want to click the “build poll” option, and then you’ll be presented with multiple buttons that’ll let you adjust your poll to your liking.
In case my explanation is confusing, here’s a step-by-step visual instruction posted to the Nameberry guidelines:
I don’t believe you have to be a member in order to build polls, but then again, it was quite a while ago when I was brand new to Nameberry and my memory has faded a bit.