Since you indicated that you do not know PHP or MySQL at all, then I will address your question by providing you with a general answer as to how this can be achieved. After that, I will provide you with my opinion why this is generally a bad idea.
1: Register event handlers in JavaScript/jQuery for the classes you
want to bind with, i.e. .item, .item.mark
2: Handle the 'click' by prompting the user to choose (yes/no) for the
target to be marked. Target here means the item being clicked.
3: Get the user response (yes/no), and preferably format it as JSON
format (JavaScript Object Notation).
4: Send the JSON data to the server (this assumes that you have your
server configured, and that you have CGI enabled or have PHP or
any other server side scripting language setup to handle the request).
5: In the server, once the JSON data is received, the scripting
language, i.e. PHP, etc.,let us say it's PHP for now, it will open and
establish a database connection (this assumes that you have MySQL
configured and setup correctly), at which point, PHP will parse the
JSON data and input the data into the database.
So, this is generally how it is done, although there are variety of ways to implement it, for example, using AJAX and such, but it follows this general pattern. Since you indicated that you do not know PHP and MySQL, and assuming that you do not know any other scripting language, it would be practical if you were to hire a web-developer to assist you with this, as this is a rather specific set of requirements that involve many other components that each require a level of expertise in.
Now, this solution does not take into consideration the detrimental security implications, that is an entirely different discussion that goes beyond the scope of this thread.
Would I implement it this way? Absolutely not. It would be helpful had you provided some technical background as to the nature of your application, i.e. server environment, do you know JavaScript/jQuery? Do you know any other scripting language? etc.
Hope this provided you with an insight that although conceptually simple, it does involve many components and consideration, including security implications and such.