The key to doing inversions is to get the tailbone or hips vertically above the neck area of the spine. Otherwise, you can’t go upside down and hold there stably.
To get up, it requires strength in the arms and core. To stay up, it requires even more. The first step is always getting up. I am very slow in this – it took me about 3 years to get my first headstand (albeit very unstable) and even longer for other poses. I simply couldn’t lift my bottom to be above my head.
A lot of core is required and it’s a good idea to prep the core region before trying anything. That said, my core is weak too, progressing slowly but surely, so it definitely took me longer to get there.
Those with strong core and arms (and a relatively smaller and lighter bum, I believe) to begin with will see progress much quicker. Could be mere months or weeks.
There are so many more inversions to unlock (chin stand, hand stand) but these are some easier ones that I can manage for now:
L Shape Handstand
Also known as a handstand prep, this is fairly easy to get into because of wall support. Despite being not suspended in this air, it isn’t less of an inversion because ultimately it’s still hips over neck.
The classic headstand. It was the first one I got up in.
Also known as tripod headstand. It’s easy for me to get in tripod with each knee on each arm, because essentially 3 points of contact on the ground is a stable structure, but to lift the legs off it requires core. It look me about 2 years to get my knees off the arms! And this is my very first inversion done in the middle of the room, without any wall for moral support or real support.
Also known as forearm stand or feathered peacock pose.