How to assign the position of f-block elements?

The f - block elements are also called as inner transition elements. As the last electron enters the f-orbital these elements are called as f - block elements. These are divided into two series. They are: Lanthanides and actinides. Lanthanides are the elements in which the last electron enters into 4f - orbital. Actinides are the elements in which the last electron enters into 5f-orbital