First, can you plug in an external monitor? If you can then you can see if the computer is still running and doing things. If you can’t then maybe you can log in via ssh? If you don’t know what ssh is then it’s probably not available, so don’t worry about it. If you plug in an external monitor and you can see the computer running and doing things, then the problem is likely the lamp in your screen has burned out. I don’t know how to replace one of these on a Mac, but it should be google-able. Hopefully you can find a replacement lamp wherever you are. If the external monitor stays black then at least your video hardware is toast, and possibly the whole computer.