I was trying to add different codes and I didnt manage to work so I give up
The getTemperature() method, when it was called printTemperature(), used to write the temperature to the LCD. Now, it no longer does. It should be relatively simple to look at the old function, and see where it is writing the temperature to the LCD. Add that function call to loop(), after each call to getTemperature().
I think it is too difficult project for me, because Im pure beginner with arduino and certainly code looks crap as my knowledge about programming.
I think you choose a project that was too ambitious, and failed to focus on small parts of the project. Reading a temperature is easy. Printing a value on the LCD is easy. Turning pins on and off based on the temperature is easy.
What is hard is trying to do the entire project without understanding anything about programming. I'm sure that if you printed out the code that you have now, and wrote all over the paper, describing what each block of code/function is doing, that you'd see that you have code that does all the "easy" stuff I listed above.
All that is left to do is organize the code in the proper order. I think that giving up at the 99% point is a mistake.