If you need to get your client's approval on a particular Task before you can continue, you can use the Client Task Approval workflow to accomplish this. When you create any new Task and assign it a Client, you will have the option to require Client approval via a checkbox that dynamically appears based on the assigned user (the checkbox does not appear if a user besides a Client is assigned).

After the box is checked, you can fill out the rest of the fields normally and save the Task. Then from the Client's point-of-view, they will see a new Task with "Approval Pending" status, and they will have options to "Approve" or "Reject & Comment" the particular Task. If "Approve" is chosen, the approval buttons disappear, and the Task is automatically given "Approved" status. Alternatively, if "Reject & Comment" is selected, they will see a box to enter their comment, the Task will change to "Not Approved" status, and the approval buttons will remain for them to approve (or reject again) the Task later. Additionally, their rejection comment will be saved and displayed in the Task history.

EThese approval statuses will be easily visible in the Tasks list for both the assigned Client, and the Admin/Manager of the Project, so you'll know quickly at-a-glance what Tasks are ready to move on, what Tasks need changing, and what Tasks are still pending approval from the Client.