Answer for this puzzle is one word. Have fun!
Highlighted parts are where I realised I have clued it wrong... Sorry for all this inconvenience!
usefulness level 1
The way of deciphering has been hinted in this post
usefulness level 2
athin should have used another colour instead of yellow. That would make things easier, hopefully...
This puzzle is a part of Ooohh, it all makes sense now! :D