from tkinter import *
def skip():
    btn_skip['state'] = 'disabled'
    btn_start['state'] = 'normal'
def start():
    btn_start['state'] = 'disabled'
    btn_skip['state'] = 'normal'
root = Tk()
btn_skip = Button(text="skip",  command=skip)
btn_start = Button(text="start",  command=start)
btn_skip.pack()
btn_skip['state'] = 'disabled'
btn_start.pack()
root.mainloop()

 skip = Button(text="Skip",   command=skip)