Do I need to know PHP to use WordPress?

No. You should be able to use Word­Press through the user inter­face, wit­hout ever having to touch PHP.

The only time you would modify your Word­Press web­site with PHP would be when inte­gra­ting some of the plugins. There are a small number of plugins that still require manual edits to your files. In most cases, clear ins­truc­tions are usually given within a text file with the plugin.

Other than that, you would not be chan­ging any of the PHP files.