The solo show is the simplest format you can follow. It's just you and the mic, talking about a subject you love. You may have title music, and you may have outro music, but often there's no need. The whole episode may just be you, on your own, talking through your material. This takes a little skill, as having just one voice on a show can become a little monotonous, depending on the presenter.
The solo show is brilliant for those that want their podcasting quick and easy. But that doesn't mean you're lazy, it can be the difference between creating consistent, quality content and petering out too early. The solo show is also great for those that want to give their listeners focussed, concise information on one topic. No waffle, no filler, just quality.