Broad match modifier may be the right match type for customers who are seeing poor ROI from their broad match keywords. It's also a good option for those who are mainly using phrase and exact match and are not receiving enough traffic, but are wary of using broad match.
As a first step, I recommend running a search term report to see what actual queries your ads are appearing on. In your Keywords tab, go to Details and select All from the SEARCH TERMS drop-down menu. If the report shows a large percentage of irrelevant queries that are triggering your ads, broad match modifier may me the right keyword option for you.
To enter keywords in broad match modifier: