file = open("text.txt", "w") 
file.write("Your text goes here") 
file.close() 
'r' open for reading (default)
'w' open for writing, truncating the file first
'x' open for exclusive creation, failing if the file already exists
'a' open for writing, appending to the end of the file if it exists

Simple way to get a directory of a file and open it:
  
from tkinter.filedialog import askopenfilename

filename = askopenfilename()