Tabs are generally used to hold the forms and their controls. You can create multiple tabs to hold multiple different forms.
Click here to learn more about creating tabs.
Forms are the structured representation of data. In Zoho People, there are pre-defined forms like Employee, Department, Designation, Leave forms, Training forms, Travel forms etc., to manage employee's information more effectively. Apart from the pre-defined forms, custom forms can also be created to build a module.
Click here to learn more about creating and customizing forms.