Robots.txt file deleted by mistake

I happened to accidently delete the Robots.txt file which was there on
my site as i did not knew what is this file for. I am not sure wat were
the contents and how it came on my site. Is this generated
automatically or provided by the hosting company?

Can i create a robots.txt file and upload it. Is it compulsory to
upload this file?

Sorry for so many questions i am new to all this stuff