Appending text via an external link

How can I insert special text into the textarea via a simple link? Here are a couple examples:

<span id="editorhelps"><a href="??">Insert A New Timestamp</a></span>
<span id="editorhelps"><a href="??">Add First Name</a></span>
<span id="editorhelps"><a href="??">Add Phone Number</a></span>

It's important to note that all of these values are fixed. Meaning, I don't need to go to another page to get this data.