The timeline visualizes Jira projects / issues as Gantt chart elements. Initially, timeline shows projects (summary tasks), tasks including progress line, and task dependencies (links). It allows to manage the tasks and their dependencies. For more details, see https://brizoit.atlassian.net/wiki/spaces/GSFJHD/pages/1373045141.
To drag the timeline left or right click and hold mouse button while moving mouse left or right.
Also, starting the app version 2.2.x, the app users can easily convert task to a milestone (purple) and vice versa, simply, by hovering over a task and right clicking and then selecting the option, s shown below.