Take a look at the Tiled files, It has everything setup there so if you're having a hard time to understand the tileset, you'd get a visual hint from there. Here is some example: 
I also recommend using tiles with transparency if possible because it's much easier to blend with other terrains
Viewing post in Epic RPG World - Grass Land 2.0 comments
Hi - the tricky thing with the transparency tiles is that it would require you to make 1 terrain layer per "type"; As far as i know, in GODOT, one tile cannot contain more than 1 texture - so you'd need a grass layer and a stone floor layer. This can begin to get complicated quickly.
For my project, I found it easier to have 1 "floor" layer and define the transitions as per your non-transparent textures. Then the next layer is "walls" (for "blocking" tiles) and then another for "props" (like trees, lamp posts or chests).
I tried the transparency layers approach and it became tricky with things like z-indexing and y-indexing when moving around. There is almost certainly a better solution than mine, but I found a simple "floor" layer easier to work with.
TLDR: please don't take away the predefined transition terrain sections ;)
If you want to keep simplicity that's ok but most games have a bunch of layers of all kinds and it's required to get a richer terrain in terms of variations otherwise you'd need a tremendous amount of tilesets transitioning to one another. The "floor" layers would be the easiest actually because this group of layers would always stay behind everything else but don't worry the predefined transitions will always be supported. GL with your projects ^^