You have two possibilities. The first methode is W3C valid but has the disadvantage that it needs javascript to work correctly. The second one isn't W3C valid (xhtml standard) but works without javascript.
1. Open up custom.js and replace:
jQuery.noConflict();
jQuery(document).ready(function(){with
jQuery.noConflict();
jQuery(document).ready(function(){
jQuery("a[href^='http:']").not("[href*='mydomain.com']").attr('target','_blank');instead of mydomain.com use your domain but without http:// or www. prefix.
OR:
2. add target="_blank" to your links like:
<a href="http://google.com/" target="_blank">Google</a>I'd recommend the first methode however because it's W3C valid and you don't need to add the target attribute to every link.
3. Alternative:
If you want to decide on an individual basis (some links should open in a new window but others shouldn't) you can use this W3C valid methode:
In custom.js replace
jQuery.noConflict();
jQuery(document).ready(function(){with
jQuery.noConflict();
jQuery(document).ready(function(){
jQuery(function(){jQuery('a[href][rel*=external]').each(function(i){this.target = "_blank";});});and add rel="external" to links which should open in new windows/tabs like:
<a href="your-external-site.com" rel="external">Your Link</a>
Create a new thread and tell me what problems you are encountering and what you want to know. 
There is no step 3 :) 
