@weberr
The features the tutorial are talking about are Convert Books >Search and Replace, at the left. That is the 'old' way to do search and replace.
The 'new' way is on the right click 'Edit Book' in the context menu in the main page of Calibre. The 'old' way was before Kovid came out with the 'Edit Book' feature. And the tutorial was written before the Edit Book feature.
Edit Book is way easier because you can watch it work, and you can tell instantly whether you screwed up the regex. Or not.
As to regexs, try the one that Kovid gave me below. Sorry, I don't know how to give you a link to that thread in this forum. Just look for 'stumblebum'.
Am I right when I am assuming you would like to get rid of a closing tag (</p>) and then the following opening tag?
Since you are playing with regexs, you probably have an idea what you are doing. It is a good one. You can fine tune it for you want to do. Just
don't hit 'Replace All' until you're
sure that is what you want. (learned from experience)
Hope this helps,
larry