First column is number of situations where a team has a runner on 3rd with less than 2 outs. Second column is the number of times they’ve scored in that situation and the third column is the percentage of times they’ve converted the situation into runs. As you can see the Cubs are 29th in baseball in conversion %.
For comparison the Nationals are tied with the Cubs for 2nd most situations and are just about at league average at converting them into runs. The Nationals have gotten 20 more runs this year out of those situations than the Cubs have.