I need to know where to start or if there is any training resources that are available to take an HTML site to a Joomla Theme and more specifically how to hook it on the gantry framework.
There is no way to 'convert' an HTML site to a Joomla site, it's a (simple or not so simple, depending on the size of the site) process of taking all your content and placing it in Joomla according to the layout you want, where you want Articles to appear, where Modules should be published, etc.
As far as'My main goal is to make the Gantry Theme look just like my current website'.
This is not going to be easy or automatic either, as you can't just move the css from an HTML site to a Joomla site (and template) and expect it to work.
The best advice I can offer; go through the templates and find the one that most closely matches your current site, then start moving your content.
IMHO, unless you plan to or don't mind spending money on customization a template to get an 'exact match' for your current site, moving to Joomla for you may be a bit of a compromise between form and functionality.
I just finished (OK, maybe another day or two) a conversion from an old HTML/CSS site to Joomla, and while the layout is exactly the same as the old site, the styling is just a bit different from the old site.
The client is over the moon with the ease of use and Joomla functionality and now that he's seen the site, although it's not an exact match to what he had before he already thinks it's 10x better than the old site.