I'm very new to coding.I have a query related to open a php file in another file. I created a php file in the name "sidebarcolumn1.php" and following are the code in the file.

```
<html>
<head>
</head>
<body>
<div id="sidecolumn1">
<div class="box_1b  box_x">
<div class="name_1 round_corner_top">New Categories:</a></div>
<ul class="list_2">
<li><a target="_self" href="/category/Site1/" title="Site1">Site1</a></li>
<li><a target="_self" href="/category/Site2/" title="Site2">Site2</a></li>
<li><a target="_self" href="/category/Site3/" title="Site3">Site3</a></li>
</ul><!--/list_1-->
<div class="slideDown">More [+]</div>
</div><!--/box_1b-->
</div>
</body>
</html>

```

Now I want to put it as a small section in main file (index.php) sidebar

How should I call the file in the header?
How should I call it in a section within ? 
How to make it fully functional code for multiple pages (as it is going to remain common for all subpages)?