List Categories and odd message in test post?! LOL

I’ve two questions …

The first being, the blog I’m working on has several categories, however, the category itself seems to be the post/page. Is it possible to list all the categories as links? I hope that makes sense!

Also, while working on the blog, the message “Activate the limitpost plugin to see the post contents !” has appeared out of nowhere! I’ve not installed another plug-in, so I’ve no idea where it came from … anyone have any idea what it’s referring to?

Thank you ??

Jennifer