It sounds like you are asking for functions that are handled by events.
Unless you mean, "...stepped on a tile with a specific terrain" i.e. any time you step on a sand tile, you are attacked by a scorpion.
or if you step on a water tile, you transport to an underwater map. (or something like that)
Inherently, terrain does nothing. It's there as an option for you to use as you wish, limited only by your creativity.
The only practical uses I've seen so far are a terrain based random encounter system,
or the vehicle system where you can only land or use your canoe, boat or dragon over certain terrain types.
As far as I know, the only built-in command that accesses it is the "Control Variable" command.
You can set a variable to a character's (player or event) current terrain. (the tile on which it stands)
so, you could have a "parallel process" event checking the players terrain, then using the conditional branch,
executing another command (battle, transport, ....) when the terrain type matches.
