You will see this theme touting a fluid width and then another with a fixed width. Some will have both for you to choose from and then you,will see other confusing words, but let's stick to the difference between a fixed or fluid layout for now.
- Fixed - Each page will be a certain size measured in pixels and could have display issues when viewed through different size browsers.
- Fluid - Allows for the site to expand or retract according to whatever browser size it's being viewed on. It's measured in percentages. Now you will also see different words like Liquid, Responsive, Elastic, and I was told they are pretty much the same thing.
It had my head spinning because I knew nothing, but I've hung around long enough and spent countless hours researching all the different aspects of building a successful site. My knowledge of how things work has greatly increased, but my technical skills in putting it all together is lagging behind.
The biggest thing to worry about is making sure your site is viewable no matter how a person reaches it in my opinion. So I think going with a fluid layout offers a better chance at achieving that goal.