For basic content edits a WYSIWYG editor is a great tool to have.  The HTML it generates, however, is not so great.  Sometimes there's a chunk of text that it just doesn't seem to want to make changes to, and the reason is usually that style tags were left behind from previous changes.  The good news, though, is it's not difficult to clean up HTML.  Doing so will restore content to its default state, and will make it respond to the editing tools the way it should.

To see the raw code of your content look for an "Edit Code" button or something similar.  Some say "HTML" or "Source."  All should take you to a window that looks similar to this:

From there you can edit the source directly, so it may be wise to copy what you have to a text editor, just to be safe. That way you can paste it back in later if something goes wrong.

The big rule of HTML is to close any tag you open. For instance in the screenshot above you'll see the paragraphs of this blog are wrapped in p tags. The sentence "This is my blog." should look like this:

<p>This is my blog.</p>

To make the word blog boldface, change it to this:

<p>This is my <strong>blog</strong>.</p>

The strong tag is opened and closed, as is the paragraph tag. The order is important, so be sure to close the most recent tag first. Don't try to close the paragraph before ending the strong tag, it will cause the editor to throw in extra tags to keep everything lined up properly.

Now, as far as more elaborate style tags go, you don't need to understand everything they are doing.  To remove the styles it's not important to know why they were there.  You just need to follow the same rule of opening and closing tags.  So a sentence that looks like this in your editor...

<p dir="ltr">T<strong><span style="color: #339966;">h<span style="font-family: 
courier new,courier; color: #ffff00;">is</span> is <em>m</em></span></strong>y 
b<span style="color: #ff0000;">l</span>o<span style="font-family: comic sans 
ms,sans-serif;">g</span>.</p>

...can be reduced to this:

<p>This is my blog.</p>

The larger version is a disaster and is difficult to read. The editor feels the same way. It tries to keep it all straight by grouping bits of the content together, but sometimes the groups change and it has to add tags to make up for it. In the end it's a mess. The above example is a tough thing to sort through, which, again, is a good reason for keeping a backup copy just in case. But pulling out the extra garbage will give you a clean slate to work with, prevent coding errors, and make your WYSIWYG editor a much more effective tool and a lot less frustrating to use.