On the Project Details or Company Details page, click on Notes & Tasks on the left-hand side of the page.
Under Tasks, click + Add Task.
Complete all the fields with an * next to them; decide who to assign the task to and when the task is due.
Toggle Visibility to adjust who can see the task.
Select Attach task to related company/contact to create an identical task for a chosen company/contact in addition to the task you have just created. 
Search for a task using the Search tasks bar on the top right. 