(sculpting) How do you quickly get a 1 million poly sphere?

I like to hop into my ancient copy of zbrush and doodle on a highpoly sphere sometimes.
Open zbrush, add a sphere, ctrl+d a few times, and start doodling.

How do you do that in Blender?

You can use dynotopo modeling which adapts the mesh details depending on you settings. If you want just subdivided sphere you can use subdivision modifier or multiresolution modifier.

How the blender sculpting work is written on official blender site https://www.blender.org/features/sculpting/ and there is a lot of sculpting for beginners on youtube for the quick learn how to start and set up your preferences.