Thumbnail views

How can I enable thumbnail views within a folder. Mine have disappeared and I can't find out how to get them back.
Thank you to anyone who knows the answer. I have
Windows 98SE.

I have Windows 98SE. I clicked on View and there was not an
option for Thumbnail. Thank you for responding.

Thank you. I opened the folder, clicked View, clicked
...as Web Page. This placed a check mark and now the side view is available. By clicking once, the thumbnail appears. Clicking
twice opens in a new window.