The Assessments tab is only available for Topics. This works in conjunction with the Assessment module, which is managed in the specific Topic's navigation settings.

On the left you will see a list of the Quiz, Fill-In and Match elements you have enabled to be part of the Assessment module at the end of your topic. This includes the question, the available answers to choose from (where applicable) and which ones are incorrect and correct. You can also see a total number of submissions and a percentage summary of which answers have been selected so far, like the example below.

On the right hand side of the screen next to the related question, you can view the list of users, their answer, whether they got it correct and when they submitted their answer.