The founder of the neighborhood can enable task reservation in the neighborhood’s settings. The founder can choose which role can reserve tasks. If you cannot reserve tasks it means that your role doesn’t have access to task reservation. 

To reserve a task, tap the blue button in the task description. An exclamation mark will appear on the reserved task's icon and will be visible to all your neighbors. The reservation will be in effect only for 12 hours.

Reserved tasks can be deleted by founders, co-founders, and elders.