Hi
There are a lot of ways to do that, it depends a lot what you want.
If you want a simple trap on the floor, you could destroy the floor actor piece when the player enters the trigger box, so the floor desapears and the player falls, or you could create a destructible actor from this floor, and when the player enters the trigger box you activate the collision or the gravity of this destructible floor, making it break in a lot of pieaces, so it becomes more realistic.
Check here to see how make destructible actors: Making a Destructible Mesh | Live Training | Unreal Engine - YouTube
To make objects fly from a wall is a little more complicate, you sould check this projectile tutorial here: A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums3-_Custom_Projectile
Also, check this Tutorials Playlists, there are a lot of good info here: https://www.youtube.com/playlist?list=PLZlv_N0_O1gaCL2XjKluO7N2Pmmw9pvhE