Firstly, you should know anyone can design and program their own web template - you do not need to use one that is pre existing.
The disciplines involved in creating a template are Graphic Design, Programming and Usability. Each one of these is a research field of it's own and basically come built-in to a well prepared pre-designed template. The time and quality advantage of using a template, depending on your skills, can be a significant bump to your online effort.
The top website development editors are Dreamweaver by Adobe Systems and Expression Web by Microsoft. For the most part, basic templates without complex nested features (like those found on this site) work well in either editor. If the description indicates "Dreamweaver Software Needed" this means it was created in Dreamweaver but will work perfectly in Expression Web and vice versa.
For most sites, a web site template is a starting point or jump-off to a new site. It is seen as a rough outline of the end presentation.
You will start with these steps:
1) Site content outline
An outline in the standard form is needed to get started:
2) Understand your web site system.
Your website system is basically the layout. This is critical in choosing a template. When looking at a template it is key to view it as a) Navigation, b) Columns and c) Information blocks. Like this:
Initial conceptual thinking in "Blocks" will allow you to choose a template more closely pre-designed to your need. You may get ideas for your site block system by viewing competitor or related sites already published on the web. It is important to maintain this system throughout your site . Doing so will create a continuity that is comfortable for your viewers and professional in design.... do not change the page layout on a whim but rather keep to your system as you assemble your site. You certainly can implement site Sections based on a different body layout but never change the header and footer as this will be very confusing to viewers.
3) Find a closely matched template to fit your "Blocks" system describes in step 2. Be not concerned with the exact colors and images as you will likely change those to your specific requirements but rather find a template that matches closely the "Block" location you need for functionality.
4) Change images, texts and navigation to suit your business or presentation.
Good luck with your new site!