Your first route should be to use a search engine for things like this rather than as a question. Also, you should include what you tried for debugging as part of your question.
As for the answer...like the error says, grunt
can't find your Gruntfile.js
.
The grunt website has a getting started page that explains the basics of the tool and then another entire page dedicated strictly to the Gruntfile.
A quick search also showed that this question and variants of it have been answered many times on this site and on other pages around the internet.
But as a summary: if you didn't create a Gruntfile in your project directory, this is the error you get. The solution is to create a Gruntfile as the grunt docs describe.