How a simple php web application works [closed]

i'm new into programming and i have a few questions: recently i download a project that use php, xampp, mysql to make a web application. Application is based on html forms, with form that have method post and action: a php file. after the user complete the form and submit, data go to php file where for example insert into database like if(isset($_POST['button'])) initialise variable and insert into database . My questions are: what architecture does that project have? i want to understand how that application work, all the architecture, what model is used, and if you can show me a diagram to understand how it works, how a simple php web application works based on files from the sistem and html forms and php code.

Thank you and sorry for my bad english!