In this first lecture, I will introduce fully extended TFTs after Baez-Dolan and Lurie, and provide an example of a fully extended TFT that has been constructed in a joint work with Claudia Scheimbauer, using factorization homology. For that matter, I will define $E_n$-algebras and factorization algebras, and present some aspects of the pioneer works of Lurie, Costello-Gwilliam, Ayala-Francis-Tannaka, Ginot-Tradler-Zeinalian, and others.