>>so im asking you to do this
Sorry, that's not the way it's supposed to work around here.
>> i dont know where to start
That's an attitude we can work with.
I'd start with a similar but simpler task. In particular I'd start with this. Using pencil and paper write down all possible 2 char strings using the following two char: a, b. Use a systematic approach that you can explain in writing. Then try all 2 char strings from the following 3 char: a, b, c. Do it systematically and write down the process you used. When you can do both of those, then you can generalize the process to the task you've enquired about. I suspect you're likely going to generate millions of strings each 4 character long from the 36 char in the problem you posted.
If you have problems along the way come back with specific questions about specific parts of the process. If you are going to post code, then be sure to read about using code tags. The information should be in the water mark of the Message box as well as at the top of the page.