How to use a jquery function from file with.js extenation

Hello,
I have a j query function I'm currently using in my page inline the code I want to be able to add it to a file I already have in the application that contains java script function
(jsfunction.js)
When Im just adding it its not working I guess I need to use somewhere
"http://code.jquery.com/jquery.js"></script> to work with the jquery libary but where?

Thank you!

<script type="text/javascript" src="http://code.jquery.com/jquery.js"></script>

      <script type="text/javascript">

   function for(){
}

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