Employee Success supports 3 types of key results at all levels of objectives i.e. company, team & individual.
Metric
Metric type of key result is numeric in nature. Wherever one needs to track numbers - be it dollars, percentages or any other unit. For a metric KR, when you are punching in the update - you just update the current value and progress percentage is automatically updated.
For example - Increase sign up rate from 25% to 45% through the iOS app. When you are tracking the progress you just update the latest value of the sign-up rate and Employee Success will automatically calculate the progress on the KR.
To do
As the name suggests, to do key results are accompanied by checkboxes. That is, they are either complete or incomplete. There is no progress percentage in between.
One example of To Do KR is - Attend Web Summit conference 2017 in SF
Jira issue
Instead of a To Do or a Metric type, if you want to make a Jira issue as a key result just search for it in the pop-up. The advantage of using a Jira issue as KR is - as Jira issues are updated, the progress of KR is automatically updated. One need not update that progress from Employee Success.
Typically, you would use Jira issues as key results in Employee Success when they do not fit in either To Do or Metric type. For example, if something needs to go through different statuses & will need action from multiple assignees.
Example - Finalise user interface designs for the mobile app - by getting sign off from 5 existing customers & keeping in mind UX field test results.