How is Html.Encode() used? What is its purpose, and how is it useful?
It HTML encodes the passed it text - this escapes things to avoid certain types of attacks, such as XSS.
For example:
Html.Encode("<script>alert('hi');</alert>")
Will result in:
<script>alert('hi');</script>
Being output to the page. This ensures that the script will not run.