Adobe Dreamweaver is a web development application originally created by Macromedia and now owned by Adobe Systems, which acquired Macromedia in 2005.
Dreamweaver allows users to preview websites in many browsers, provided that they are installed on their computer. It also has some site management tools, such as the ability to find and replace lines of text or code by whatever parameters specified across the entire site, and a templatization feature for creating multiple pages with similar structures. The behaviors panel also enables use of basic JavaScript without any coding knowledge.
Dreamweaver can use "Extensions" - small programs, which any web developer can write (usually in HTML and JavaScript). Extensions provide added functionality to the software for whoever wants to download and install them. Dreamweaver is supported by a large community of extension developers who make extensions available (both commercial and free) for most web development tasks from simple rollover effects to full-featured shopping carts.

The class selectors which can be applied multiple times to different element  within a page to format content.
Using CLASS selectors in CSS one can assign style information to all elements. Class selectors name in CSS is preceded by full stop.

 The Multi-Column feature of CSS3 the web designers can get their output in multiple columns with definitions defined for each column like column-width, column-count.

Using the following way you can set two classes.

<p class="first second">

it will apply two css class named first and second.

A:link { text-decoration: none } ----- for normal, unvisited links, no underline;
A:active { text-decoration: none } --- active is for link appearance while you're clicking
A:visited { text-decoration: none } --- visited is for previously visited links

Stylesheets, as the name suggest, define styles (look and feel) for the content that HTML holds. One can re-use same set of CSS styles over number of pages throughout the website to keep a consistent look and feel. Stylesheets help web designers keep the HTML clean and separate styles from the content.

The question is not entirely correct in its sense. There are HTML elements which you can float with the help of CSS e.g. a DIV element or text/image inside an HTML element. You can use float:[left | right]; property to float HTML elements inside its own container (i.e. its parent element).

Choosing between External, Embedded and Inline CSS is critical. It is always advisable to think long term. Even when you are working on a smaller module, you never know its future. Moreover, one must remember that CSS is all about 'look and feel' (style) while HTML is content; so better keep them separate.
As far as possible, avoid Inline styles. If you are very sure that particular CSS classes are relevant only to the current web page, it might be a good idea to opt for Embedded under certain circumstances. And ofcourse, there are no cons while considering External stylesheet.
One thing is very important while using External stylesheets is the nomenclature. There are no fixed set of rules to follow but if you consider a broader view, you can easily work out a fair plan for CSS class names.
To start with, one can study some popular websites.