Open the Use Case Specification window and click the Use Case Scenario property group.
In the Basic Flow area, click the Add new step button or press Alt+ENTER and type a name of the basic flow step. Repeat this action for each basic flow step you need to create.
Steps of the basic flow are numbered automatically. Use buttons Up and Down to change the order of steps. In the activity diagram, steps are represented according to the ordering in the Use Case scenario.