The press to handstand is an impressive feat to pull off and requires a lot of core strength as well as a solid handstand at its base. If you are trying to achieve it, these videos give some really useful hints and drills to work up to it! Good Luck!
Secrets of the Press Handstand by Movement Parallels Life
Dave Durante works Press Handstands with CrossFit Games Champion Katrin Davidsdottir by PowerMonkeyFitness
A bit of my progress: