You should take a look at the PHP Manual, and read more about str_replace. What that function will do is replace a searched string with a string that is set up for highlighting.
Note, that to get words to highlight all you will need to do is pass your url like this:
If term is on the page, which I will assume you are getting from a database (be sure to query and get the pages data, and change $your_page_content to the string with your content), this will then allow the following piece of css to highlight the term.
(This CSS code has to be on every page between the <head> and </head> tags:
That will cover and highlight the term that you selected with a yellow background, you can adapt it to your purpose.
--- As for the searching for " ---
This is simple, but again, if you need to search for it, try the term /" (that is / and then "), in php, some characters are special, so you have to escape them, or else your script will spit it back at you.
str_replace () was good, but it is case sensitive so some results where not highlighted. Searching in the web I found a good solution that is not case sensitive. I'll post it, maybe it's useful for someone.