This blocks directory is where to put any block image PNG files from your "\assets\minecraft\textures\blocks" directory in a Minecraft resource pack in order to create your own terrainExt.png file, which Mineways' File | Set Terrain File then uses.

Note: in 1.11 on, you also want to copy the (rarely seen) barrier.png tile in "\assets\minecraft\textures\item(s)" to this blocks directory.

Finally, from your resource pack's "\assets\minecraft\textures\entity\chest" directory and put the chest images ender.png, normal.png, normal_left.png, and normal_right.png (or normal_double.png, for resource packs for 1.14 and earlier) into the "chest" subdirectory here.

See mineways.html (in the docs directory, or http://mineways.com/mineways.html#tilemaker) about the TileMaker for more information.