I do not believe one needs to know anything much about php to use wordpress. It helps but it is not necessary.
And I sometime get frustrated with wordpress, especially since I expect the entire world to be point and click, right now!
I used to like plain old html until this mobile deal started and as it turns out wordpress can handle it.
Another problem with plain old html and css was adding pages and editing menus and navigation.
With wordpress it's a snap and I do not have to change a million pages.
That said I find that using php for headers and footers and navagation on my html pages really saves a lot of time.
Just simple bits are a big help.
There is a ton of information online for editing wordpress.
Just search for what you want to do, for example, "create a child theme" or "move sidebar to left wordpress twenty ten".
The answers are usually fairly easy to find.
like anything the more you use it the more you will get used to using it. I often forget how to do this or that but I can usually find the answer here or by doing a quick search.
I used to grab off the shelf themes and change them to my liking but I became paranoid that someone put something odd in the code somewhere so I now just take one of the stock themes and make a child theme.
I also find it is easy to show someone else how to edit their own page with wordpress.
I have setup a number of pages for businesses and groups of one kind or another so that people can make some changes as they need.
Not to say they edit the theme but to change things that need changing from time to time.
There are a number of really useful free or paid plugins to do everything from soup to nuts for wordpress.
But, sometimes there is a nut can't be cracked with wordpress and so I fall back on html, css and php.