A Milestone in Qase allows you to create a specific point in your release or development cycle that can be later used to attribute your Test Cases, Defects and Test Runs. In other words, you can specify which release or version a Test Case, Defect or a Test Run "belongs" to, which sprint a Test Run has been executed during, or which sprint a Defect was discovered in.
To create a new Milestone, navigate to "Milestones" section, and hit "Create Milestone":
From here, give your Milestones necessary attributes - a Name, brief Description, Status (Active or Completed), and a Due Date:
Now that a Milestone is created, you can select it to be applied when creating a new Test Case, Defect or Test Run, or edit the existing Test Cases, Defects, and Test Runs to be connected to this Milestone:
Once your Milestone has been assigned to a Test Case or several Test Cases, you will see how many Test Cases it has been assigned to in the "Milestones" section:
You can also sort your Milestones by clicking an arrow next to a column's name: