Can I create a form and have multiple users fill out different sections of the same form?

And another question is: I want an employee to fill out (let's say) form A with all the questions. Then the employer gets the employee information automatically out of this form A and need to fill in some more question in form B which are not visible for the employee. After that, we get all the information from form B. 

Yes it possible to achieve your requirement by taking advantage of a combination of our conditions, widgets and edit link feature.

You may like to take a look at the following guide which should help you:   https://www.jotform.com/help/432-A-General-Approach-on-Building-an-Approval-Process-Workflow 

Do try it out and get back to us if you have any questions.