Automatically floating two columns next to eachother is not currently possible only with CSS/HTML. Two ways to achieve this:
Method 1: When there's no continous text, just lots of non-related paragraphs:
Float all paragraphs to the left, give them half the width of the containing element and if possible set a fixed height.
<div id="container">
<p>This is paragraph 1. Lorem ipsum ... </p>
<p>This is paragraph 2. Lorem ipsum ... </p>
<p>This is paragraph 3. Lorem ipsum ... </p>
<p>This is paragraph 4. Lorem ipsum ... </p>
<p>This is paragraph 5. Lorem ipsum ... </p>
<p>This is paragraph 6. Lorem ipsum ... </p>
</div>
#container { width: 600px; }
#container p { float: left; width: 300px; /* possibly also height: 300px; */ }
You can also insert clearer-divs between paragraphs to avoid having to use a fixed height. If you want two columns, add a clearer-div between two-and-two paragraphs. This will align the top of the two next paragraphs, making it look more tidy. Example:
<div id="container">
<p>This is paragraph 1. Lorem ipsum ... </p>
<p>This is paragraph 2. Lorem ipsum ... </p>
<div class="clear"></div>
<p>This is paragraph 3. Lorem ipsum ... </p>
<p>This is paragraph 4. Lorem ipsum ... </p>
<div class="clear"></div>
<p>This is paragraph 5. Lorem ipsum ... </p>
<p>This is paragraph 6. Lorem ipsum ... </p>
</div>
/* in addition to the above CSS */
.clear { clear: both; height: 0; }
Method 2: When the text is continous
More advanced, but it can be done.
<div id="container">
<div class="contentColumn">
<p>This is paragraph 1. Lorem ipsum ... </p>
<p>This is paragraph 2. Lorem ipsum ... </p>
<p>This is paragraph 3. Lorem ipsum ... </p>
</div>
<div class="contentColumn">
<p>This is paragraph 4. Lorem ipsum ... </p>
<p>This is paragraph 5. Lorem ipsum ... </p>
<p>This is paragraph 6. Lorem ipsum ... </p>
</div>
</div>
.contentColumn { width: 300px; float: left; }
#container { width: 600px; }
When it comes to the ease of use: none of these are really easy for a non-technical client. You might attempt to explain to him/her how to do this properly, and tell him/her why. Learning very basic HTML is not a bad idea anyways, if the client is going to be updating the web pages via a WYSIWYG-editor in the future.
Or you could try to implement some Javascript-solution that counts the total number of paragraphs, splits them in two and creates columns. This will also degrade gracefully for those who have JavaScript disabled. A third option is to have all this splitting-into-columns-action happen serverside if this is an option.
(Method 3: CSS3 Multi-column Layout Module)
You might read about the CSS3 way of doing it, but it's not really practical for a production website. Not yet, at least.