I like tinkercard it is very informative.
Conquer 2-4 Tinkercad quests. Learn basic navigations, make a batman badge, or even making a ring (in less than 5-10 minutes!!)
To make an egg holder in openscad, use cylinders to make a simple base and for the egg-holder intersect two spheres with the "difference".
To make the pendant with a hole, use again "difference" with a cylinder and the pendant you design, remember that your cylinder must pass through the pendant side to side.
To use difference in openscad with any two solids:
I completed a total of 20+ quests! I love them and love discovering techniques through these quests. That is the no.1 advantage of Tinkercad, letting you tinker other people's creations! You can learn very quickly by doing.
My favorite quests? Hard to say, I tried one of each kind: jewelry, egg, dice, heart shape... it depends on what you ultimately want to make, you can explore what will lead you to completion faster.