The next step is to work out what things will clearly indicate whether you're moving towards, and ultimately achieving, the goal you've selected. That process determines the way you're going to do the actual work of realising that goal, what will add value and see meaningful progress.
Key Results should be metrics — they're things you can measure, things where you can see your effort moving the dial. Usually that means they're things with a number, but not always. Key Results can be relative numbers like 10%, absolute numbers like 50,000, binary results (yes/no), or one of a series of milestones.