How do I assign a property? and how do I assign density? Can someone please give me some instruction on how to begin?

in the tree manager select select configuration manager(start from left side third one on the top)
then right click and select from the menu (add configuration)
then give a name as you like , you can repeat that as much configurations as you need.
then activate the configuration that you want by double clicking it ( you will see green check)
start making changes to you part all changes will apply for that config only , this is just brief explanation and you have to practice more to get familiar with config.
it's very useful option
I hope that I gave you a good start point to begin with

Click "file>properties" to open the properties window which allows you to select existing/define new properties and assign values to them.

Your Design Tree should only have the 3 features shown in the properties picture attached. The center hole should be made with the initial revolve. Reference revolve Sketches shown below. Your extrude cut and additional sketch is not needed. The hole position can be defined as shown in attached picture.
To add custom properties you need are added through the file properties menu on the custom tab. Properties are shown in attached picture.