Adding a new task
Add a new task by clicking on the "+ NEW" button.
Enter a title for your task and add text that describes what needs to be done in the task. This will also be the first comment on your task.
You have several text formatting tools at your disposal (bold, italic, code, list, numbered list).
If you need to attach some files to the task, use the Insert attachment button. Select and upload files from the dialog window or simply drag and drop files into the text input section.
Use @ button to mention someone (just like on Facebook). That person will be notified that there's something in the task requiring their attention.
NOTE: the person you want to mention needs to be a project member.
Choosing a task list
Now that you have a title and a description select the task list for your task. You can select it from the dropdown menu, or if you don't have one yet, simply start typing the name of the task list you want to create and select the Create task list option.
Assigning tasks to people
You can assign a task to someone on the project. Use the drop-down menu and start typing the name of the person you want to make in charge. Like with mentions, the person needs to be a project member.
Sometimes, it could be useful to add tags to your task. You could enter something like "design" for all tasks that are design-related, or "sprint w2" for tasks that were planned for week 2. Tags come in very handy when you want to set up your custom filters.
If you're on a tight schedule, set a due date by which you need this task to be done. The person who's assigned to this task will get a notification 24 hours in advance of the due date, and it will also show up in their "My overdue tasks" filter section.
Besides mentions and assignees, you can add subscribers to the task. If you want certain people on the project to be notified when something happens in the task - like someone adds a new comment or changes the assignee - add them via the Subscribers menu.
Like with mentions and assignees, the person needs to be a project member.
Don't forget to hit the Create task button when you're all done filling out the form.
Create a private task on your project that is visible only to you and the people you add to the task (subscribers).
Look for the lock icon in the upper right while creating a task.
If the icon looks like in the picture above, that means the task is not private and everyone on the project can see it.
However, if you click the lock you'll enable private mode and the task panel will change its background color.
This now means that this task is private and only people you add as subscribers will be able to see it. The rest of the project members won't see this task until you assign the task to someone or add them as subscribers.