The TinyMCE editor is a WYSIWYG editor (what-you-see-is-what-you-get). This means that instead of needing to write html code, you can manipulate your text using an interface that's familliar to anyone who has used an email applications.

Here are some of the basic functions you can perform:

Bold, Italic, Underlined, and Strikethrough: Simply highlight the text and select the appropriate button.   

Left Justified Text, Centered Text, Right Justified Text, and Fully Justified Text: Simply highlight the section of text and select the corresponding button.

Bullet and Numbered Lists: By selecting the corresponding button, an indented bullet or number will appear on the next line.  After that, each time you hit enter another will appear below it until you deselect the button

Undo and Redo: These should be self-explanatory, but you can undo your mistakes by selecting the backwards arrow and then, when you realize it was the right thing to do after all, you can redo them by selecting the forward arrow.  

Insert Link, Break Link, and Insert Anchor:  Using these buttons, you can add hyperlinks to your texts.  The chain link icon allows you to create links, the broken chain link icon removes your link, and the anchor icon creates link destinations within pages (ie, if you want your reader to jump to a point near the bottom of your text).

When you choose to create a link, you will be presented with this box giving you options (see right). Here, insert your desired link destination. Using the target menu, you can also indicate whether you'd like you're link to open up in the same window or to open in a new window.