Can someone tell me the difference between a Photoshop template and an HTML template and what is the advantage of one over the other. I noticed on some Photoshop templates, it looks like some stuff is editable and some is not. Do you have to look around and find something with the same theme as what your site is?

I dont completely understand your question, mainly because a photoshop template will have to be turned into an HTML template to be viewed.

A photoshop template simply by itself is just an image (a .psd to be exact). An HTML template is a template that has been coded, probably from an existing photoshop template.

To sum it all up (it pretty much is already, but meh)

A Photoshop template is an image created in Photoshop.

An HTML template is an actual template that is coded and ready for use.

A photoshop template is indeed just a photoshop file .psd which you either can make yourself if you have some designing skills, or you can buy/download somewhere.

The main difference between the 2 is that within photoshop all elements are still moveable and free to edit to your own liking. Once it's in HTML things are all in "boxes" and if you would want to switch the header with the footer for instance, it wouldn't be a matter of a few clicks but a matter of building an entire new layout.