how to create a new tile

[Lutra]

i am trying to add a new tile, just to see how it works. i have looked at the API and at other mods, but still don't quite understand how to add one. is it as simple as adding an item i.e using data:extend or is there a specific method? also what does the collides_with method mean? is this what layer the tile is on-if i wanted to add a water tile do i make it collide with water or collide with player? thanks in advance