In Typo3, what is the difference between setup, constants, and TSConfig

Question

It seems there are three different places where I can write TypoScript: in templates, there is the constants field and the setup field, and in each page, there is a TSConf

Answer 1

• TSconfig is mainly for the backend configuration. You can add/alter/remove values from forms, change the behavior what kind of records users can add, default usergroups etc. see About TSconfig for more details.
• Typoscript in the template is used to change the frontend behavior, template parsing, Extension configuration, navigation etc. Typoscript in the template has so called cObjects which provide useful functionality like Image manipulation (IMAGE), getting records from the database (RECORDS), creating menus (HMENU), see TypoScript Reference.
• Typoscript constants are much like variables, which can be used within your template Typoscript. e.g. you have an email address which occurs in many different places within the Typoscript template, you might want to define it as constant. See documentation for more info.