Sass is a scripting language that is interpreted into Cascading Style Sheets (CSS), also known as a preprocessor. If you can write CSS you can start using Sass, and begin taking advantage of the benefits it offers like variables, nested rules, mixins and many other features that enable quicker front end development.
The Sass @for directive is a pretty powerful feature. It’s really handy for iterating over a set of items. The directive has a pretty simple format: @for $var from <start> through/to <end>, where the from/through variation includes all values, including the last item, and the from/to variation doesn’t. It’s been around since the 2.2 release, however, I just recently got my first chance to work with it.