—Information accurate as of: build 904.83
You need to place a Floor Frame and then place the Ladder Hatch inside of it, much like the Wall Frame. Although the Ladder Hatch is resistant to damage from most melee weapons, tools, and bullet damage, it is extremely vulnerable to explosive damage. The cheapest method of taking out a Hatch is 1 Rocket and 3 Beancan Grenades. Lock can be placed on an open or closed Ladder Hatch.
The Ladder Hatch can be crafted at a Work Bench Level 2 with:
Jumping while on a ladder hatch makes you go up faster.
Holding the jump key while going down a ladder hatch takes you down quickly.
Putting a Snap Trap under the top of the hatch will hide it and will trap anyone that walks on it