I am very new to webdevelopment. I've been given this task to built an application to calculate final salary in the end of the month.
The employees are callers and after every call they will get some form on which they will give their call summery like time duration. They are payed for each call depending on time duration.

In the back end there will be sql database and some code to calculate the the final salary. Current they have to calculate the salary manually, they are just using google docs form.I have some idea that i need php in the front end sql in the back end but i am not clear about the whole picture please can someone give me a clear skeleton.

My main question is what to use to calculate the salary from the database??And what should i use to create a front end form ??