Edit: Double click on a paragraph to open the editor. Change as you see fit. Use Command-S to save or just move on to another place. The save is then automatic.
Create: Make a new paragraph by clicking on the [+] at the bottom of a wiki page. This creates an almost-paragraph called a factory. Drag it to where you want your paragraph and then double click it to start editing as above.
Split: Press the Return (Enter) key to start a new paragraph while editing an existing one. Try this in the middle of a paragraph to split it into two. Press Delete to rejoin split paragraphs.
Delete: If you save an empty paragraph then the paragraph will be removed, including the identity that connects it with earlier versions elsewhere in the federation. See also How To Remove Paragraphs.