Here are some ways to use HTML tags to change the look of text in your blog or add a hyperlink in an area that doesn't have the option for hyperlinks (many areas do have the option to make something a hyperlink).
To change the text size, font, and color (if you didn't want to do all three, just eliminate that part of the code):
<span style="font-size:16pt;font-family:arial;color:purple;" >This text is larger, Arial, and purple</span>
This is how the code above will look:
This text is larger, Arial, and purple
Remember to make the font-family a common font that you can find on both Macs and Windows computers. Otherwise, the text will display as the default font. Also, use common colors.
To insert a hyperlink:
<a href="http://thewebsite.com">The hyperlinked text</a>