Your buildings are really good OvO
for the worlded part, you need two bmp:
one should be called "whateveryoucallit.bmp", you put things like dirt, roads, water(river,pond), grass floor tiles here
another one should be called "whateveryoucallit_veg.bmp", it is for vegetation. the background should be black, and layers from your screenshot above "normal trees" "grass on dark grass" should be placed at this bmp.
Each grid in worlded is 300x300pixel, hope you know what I mean
These two bmp need to be at the same directory. Than drag "whateveryoucallit.bmp" to those grids, you should see your map is placed there immediately.
Then go to File -> BMP to TMX -> All cells / Selected Cells only -> choose a export directory -> check the two on the bottom left -> click OK
click on a grid, and you shoud be seeing part of your terrain and be able to place buildings on it.