from tkinter import *

def add_name():
    name = name_box.get()
    name_list.insert('end', name)
    name_box.delete(0, 'end')
    name_box.focus()

def clear_list():
    name_list.delete(0, 'end')
    name_box.focus()

window = Tk()
window.title("Lista Nombres")
window.geometry("400x200")

labell1 = Label(text="Agregar:")
labell1.place(x=20, y=20, width=100, height=25)

name_box = Entry()
name_box.place(x=120, y=20, width=100, height=25)
name_box.focus()

button1 = Button(text="Agregar", command=add_name)
button1.place(x=250, y=20, width=100, height=25)

name_list = Listbox()
name_list.place(x=120, y=50, width=100, height=100)

button2 = Button(text="Borrar", command=clear_list)
button2.place(x=250, y=50, width=100, height=25)

window.mainloop()