You can copy estimate items from cost books, job templates, or other jobs. To do that, please follow these steps:
Open the job you want to copy to.
Tap (or click) the + button in the upper right to add an item.
Select one of the options in the "Copy Items" section.
Navigate to and select the item or item group to copy.
Select either "Copy All Items", or "Copy Group" (for group items), or "Copy Item" for individual items to copy the item(s) into your job.
For more information, here is a video about creating estimates in ContractorTools: