After issues are created in a project, they need to be linked to show relationships between them. Linking tasks creates issues dependencies. There are two ways to link tasks:

• Using JIRA Issue editor, you can find the explanation in JIRA Documentation.
• Using Gantt-Chart view to create interactively. 

JGCP supports all four types of issues dependencies:

A link will be displayed if two connected issues present in diagram.

Finish-to-Start Dependency

The dependent task (B) cannot begin until the task that it depends (A) on is complete. If B is unscheduled issue, its start date will be displayed at the end of the issue A.

Start-to-Start Dependency

The dependent task (B) cannot begin until the task that it depends (A) on begins.

The dependent task can begin anytime after the task that it depends on begins. The SS link type does not require that both tasks begin simultaneously.

Start-to-Finish Dependency

The dependent task (B) cannot be completed until the task that it depends on (A) begins.
The dependent task can be completed anytime after the task that it depends on begins. The SF link type does not require that the dependent task be completed concurrent with the beginning of the task on which it depends.

Finish-to-Finish Dependency

The dependent task (B) cannot be completed until the task that it depends on (A) is completed.The dependent task can be completed anytime after the task that it depends on is completed. The FF link type does not require that both tasks be completed simultaneously.