You can identify previous or following tasks, on the same section or group, as ''Parent'' or ''Child'' of your current task to show the dependencies between them.
To add dependencies you must open the task and click on the Dependencies button. It will display the other tasks on the current section or group, with the options for you to select ''Add as Parent'', or ''Add as Child'' respectively.
On the Gantt Chart of your project, you can add dependencies by clicking on the arrow icon that appears on the right side of the task when you hover over it.
After clicking on the arrow, select the ''Child'' task. That is the task that will depend on the originally selected task.
It will display an arrow linking the dependent tasks.