To create a reusable task (a task template), open the Tasks page, and make sure the filters are set to shown:
At the bottom of the side panel, below Task Options, you will see the Task Templates section:
Task templates can be made in one of three ways:
Click the Add button in the Task Templates box, or
Right click on an existing task and choose Convert to Template, or
In an existing task's page, near the bottom of the page, click on Convert to Template
Add button method:
Right click method:
Once a template is created, you can edit it using the edit button next to it:
This will open the template editor.
Just fill in the fields and you are done. Note that the Billable section will show only if this is a client-related task, or if you specifically mark it as Billable.
Also note that the Global flag is checked by default. That means that this template is available globally. If you do not want the template to be visible to others, uncheck this flag.
Once the template has been saved, you can create a new task based on the template by clicking on the Add button:
This will create a new task in a modal window that you can quickly tweak and save.