This is very easy to implement and I will walk you through the steps.
Step 1) Make a new file with some functions you want to use in your script, but that you want out of your way. For my example, I will make a very simple example, so my file will only have 1 function and 1 value:
#A variable we can call from our other script.
test_var = 100
#Print whatever the input is
def print_input(input):
print "Input is: "+str(input)
Now that this file is created, save it as "print_functions" or another appropriate name that is easy for you to remember. You will need to know this name for importing.
Next, create a new Python file. This file HAS to be in the same directory as the other one, or you won't be able to import the other file. This new Python file can be your active MyScene script, or anything you want really. At the top of the new file, put this line:
from print_functions import *
What this says is to import everything in print_functions. So you can now call the print_input function or find the value of test_var from your other script, after you have imported it:
print_input(10)
print test_var
If you wanted to keep your print_functions OBVIOUS they're in the print_functions section of your code, you could import your module differently:
import print_functions
print_functions.print_input(10)
print print_functions.test_var
or...
import print_functions as pf
pf.print_input(10)
print pf.test_var
If you only need a specific function for your current script and you don't need all the functions available, it's a good idea to implicitly state which functions/values you need. This way, your program doesn't have to compile a lot of useless 'garbage' before it runs:
from print_functions import print_input, test_var
print_input(10)
print test_var
Personally I suggest the first method. It imports everything. You only need to import a script once, then the functions will be useable throughout the rest of the script - regardless of what your script is doing, it will work.