It is complicated.
Unless an API is available (which is very likely), at first you have to make a request to the server and get all the HTML from the server:
// This function fails if outside requests are turned off on the server
Then you have to use regular expressions to parse the returned HTML and find the information you are looking for. Google for preg_match() function and you'll find a lot of examples. Regular expressions are a complicated topic and they are different based on how the information is stored that you are looking for.
With regular expressions you can find any data you need from a string (HTML string in this case), but you have to write the regular expression yourself that works with that specific website.
Also, if they update their website then you have to (most likely) rewrite or tweak your regular expression a little.