Yes.
That depends on your abilities and particular approach.
What have you tried?
Very Likely… Did you look?
Then Might I recommend going to your nearest Barnes and Noble (or your favorite bookstore or even Library) and getting a book on PHP. I personally liked Beginning PHP 4 from WROX press. http://www.wrox.com/books/0764543644.shtml.
Next thing you should be aware of is that if I understand your “somewhat vague” question, you probably want to use Javascript. PHP presents STATIC pages that are created Dynamically. You can certainly incorporate Javascript into them. This would give you the flexibility to use ON-CLICK events and update totals, whereas PHP (a recurssive acronym for PHP Hypertext Preprocessor) only presents the page directly from the server. If you want PHP to do the job, it can, however, you would have to send a complete updated page for each event. Unless you have a site that is not busy or have huge bandwidth, this is not the most efficient way to do it.
Your welcome.