<p>Could anyone recommend to me a good online guide to PowerPoint VBA? Also, does anyone has advice on how to record a macro in PowerPoint? </p>

To record a powerpoint macro:
In the menu bar, click on Tools
Mouse over Macro >  and the submenu will be displayed
Click the Record button - a new toolbar will be displayed
Do your thing
Click the stop button on the new macro toolbar
Click on Tools->Macro->Macros.  Find the macro you just recorded and click the Edit button.  That will show you what was recorded.  Make your modifications and click the triangular run button (or push F5) to run your code.
As far as an online guide, I usually think of a question and use
Google
or ask a question here on StackOverflow.com.  I've been able to answer most of my questions that way, I haven't found a particular main resource for all things Powerpoint VBA.
Also, you can find answers that can help you by looking into VBA articles for other MS Office products - a lot of things that are not Powerpoint-specific (general VBA) will be the same as for the other products.