It is good practice to group tasks per feature or job, which consist of several tasks. Splitting tasks into subtasks makes the project more clean looking and well organized. In addition, having projects clean and organized increases your chances of delivering the project on time and within budget.
Assuming that you have project tasks prepared on paper, in an electronic document, or in your mind, the first thing to do is create a standard Redmine issue with a type of Feature, Task, or any other custom issue type that you customized, which will serve as a parent task:
On the parent task that you just created, click the Add link:
The Issue entry form will open up. Fill it with your issue details. If you are adding more sub-issues in a row, click Create and continue. A new Issue entry form will load with the Parent task field's value preloaded:
When you are done entering subtasks, navigate to your parent issue, and you will be able to see all of this...