(ultrasonic sensor code : No such file or directory)
It means what it says:


  Ultrasonic.h: No such file or directory


The file Ultrasonic.h can't be found.

Anything in your code that starts #include... is usually a library. These are third party pieces of software that you have to obtain and install into the relevant location (See Installing Additional Arduino Libraries).

Some libraries are bundled with the IDE, and some are available through the "library manager" in the IDE. However most aren't, and you will have to get used to finding those libraries and installing them.

The location you got your example code from will most likely link you to where to find the relevant libraries to get the code working.