There are multiple ways to get into balancing upside-down: you can balance off the wall, you can jump straight into it, you can press into it from the ground, or you can split your legs. That last one is generally easier. To do that, place your hands on the ground, lift one leg up, and jump off the other one, then slowly bring the legs together at the top.
To be able to balance, you will need to dig your fingertips into the ground, so that your center of mass is on a line somewhere between your wrists and your fingertips.
This exercise is a valid progression towards the straight-body Handstand . Contrary to some beliefs, it is not bad for your back, because there is no load placed on it.
Risks
Make sure you are comfortable falling before attempting this exercise without a wall. When falling because of overbalancing (too much weight forward), the easiest way to get out is to "pirouette", which is done by moving one hand forward (generally your dominant hand), and do a motion resembling a cartwheel.
Make sure your can hold your weight up before attempting, to avoid falling head first on the ground. A 30 seconds-long Back-to-wall handstand is necessary.
As with most handbalancing exercises, this creates a lot of tension in the wrists - make sure they are well warmed up before practicing, to avoid getting hurt.