Assessment definitions provide the basic structure of any assessment: the number of questions, the value of each question, the correct answer (if applicable), and any objectives that are tied to the assessment. The assessment definition does not include students or results. If you're interested in copying students and results, please see this article.
Using the "Action" menu, download the definition from an existing assessment. The file generated is a .csv that you can save and upload into new assessments via the import box, allowing you to use it as a template within your school or even at other schools in your network, as in the example below. Remember that you still have to fill in basic assessment info like name, type, and course.
Be aware that objectives will only be recognized if you're uploading the definition into a course that has the same exact objectives as the original course from which you took the definition. Otherwise, you'll see a message like the one below, which indicates the objectives in the definition are not linked to the course you've selected (depending on your settings, this may not actually add new objectives - see here to review the relevant setting).
To upload your assessment definition, go to the Add Assessment page to create your new assignment. Drop your .csv definition file into the Import tab:
Once the definition has been successfully uploaded, you only need to enter student results and save! The same definition can be used over and over again.