• Type the command /todo in a Slack channel and hit enter.  The task composer pane will appear.
• Click on the drop-down menu under Space and choose the space/channel for your task.  
• The task will be set to be created in the default list in that space/channel.  To change lists, click on the arrow next to the list name, and choose the preferred list.
• Type the task title in the Summary line.
• You can add a task description in the Description section.
• Click the drop-down menu under "Assign to" to assign the task.
• Enter a due date either by using the drop-down menu.  Add a due time the same way if desired.
• Once you are finishing creating your task, click Create.