You have to use a build tool like Gulp which will convert the SASS file to CSS file , then you just have to link the CSS file in your HTML.
What’s interesting is that you don’t have to do this everytime you make a change in your SASS file. Gulp has a watch function which monitors the SASS files for changes and generate CSS file on the fly.
To use SASS with gulp , follow this tutorial - http://ryanchristiani.com/getting-started-with-gulp-and-sass/

Aditya Agarwal