Adding or modifying text is the simplest thing to change on your page, and will be made even simpler if you're using notepad++ (see tools/tips) as webpage text will be shown in black.

An example is shown below so I can explain this easier.
The colored text (items with <> around them) are tags, these are what tells your browser how to show the page and where to place the content. Any text in black (without tags) is webpage content. This is content that you can modify.

Another thing to mention is on line 7: the <br/> tag marks a new line. Two <br/> tags will start a new line, then another new line leaving a full blank line between paragraphs. Without these tags, text will continue to stay as one paragraph.

Also note the <strong> and </strong> tags on lines 2 and 10. Placing text between these tags will make the text bold and add special formatting. Each webpage's "strong" will be coded differently, so make sure you check this after setting it to make sure it looks the way you had hoped.