inserting content into node using field I am really stuck and need some advice, I'd like to know how I can go about doing this, simply put:

A website contributor enters a value into a field which is placed into the html.

eg. I have say two fields that will determine an image name and the file type. In field 1 the user enters [ABC], in field 2 the user enters [123].

The output of this would be &lt;img http://www.example.com/[ABC].[123] /&gt;

I have never worked with my own custom modules/fields etc before, a point in the right direction would be a big help.
To do this in a template, 
1. create a file inside your /sites/all/themes/YOURTHEME folder, called node--CONTENT_TYPE.tpl.php.
2. copy the contents of node.tpl.php into that file.
3. add something like the following to the template file, where you want to print the image:

&lt;img src="http://example.com/&lt;?php 
    print $node-&gt;YOUR_FIELD_1[$node-&gt;language][0]['value'] . 
    '.' .
    $node-&gt;YOUR_FIELD_2[$node-&gt;language][0]['value']; 
    ?&gt; 
 alt="..." ... &gt;


Another possibility (probably better), would be to use the filefield sources module, and let the users upload the image to your drupal site by pasting the url.