It depends of what you’re trying to accomplish. If you only want to install WP and add a theme and some plugins, it will be really easy to do so. If you do this and only want to make some adjustments, you could easily google what you need, because there is a lot of documentation around PHP.
If you’re trying to code your own WP theme, things get nastier. To make it easier for you, download some existing themes and check out the code in them. Most of code will be HTML and CSS, because PHP is only used to generate the dynamic content, like posts, comments, sidebar contents etc.
You could just create the HTML and CSS for your theme and get the PHP parts from an existing theme.
You can read here about theme development and here you have the PHP manual.
Here you have a list of themes used as boilerplate for development: 1, 2.