Structure.Gantt uses Jira issue links for working with dependencies between issues. Dependencies between other types of items, such as folders and pages, are also supported, but stored within Gantt itself.
For issue-to-issue dependencies you will need to specify a link type for every type of dependency you want to use.
Gantt plugin creates a link of the corresponding link type between issues when you add a dependency via Add Dependency dialog or with drag and drop.
By default, "blocks" link type is used. If the BigGantt app is installed, it is set to "Finish to Start" link by default.