What is the difference between Content page template vs Content page type vs Content page item.

Basically i am new to learning Kentico CMS. In my knowledge Content page template can be used to create Main page type in which these types of page types are allowed and we can create page types of specific types and item means when we need to insert some multiple entries like in the database we need to create content item.

And Content template is basically is a standard page type.

And Content page type with container is just like a component with empty container in which multiples web parts and widgets can be dropped by adding widget zone or web part zone.

Please confirm my knowledge.

And one question how many types of Content page templates can be created and why we need to create multiples page types when one page templates can have multiple properties and we can have null check in our codes is it related to layout.