What happen exactly when I enter URL in the browser and press enter? [on hold]

I would like to know what exactly happen (also behind the scenes) when I enter URL address in the browser and press enter ? and also how is that different (if there is one) when the web is build on PHP (server side) and Angular JS/Ajax (on client) ?

The regular client-side technologies are also in use: HTML, CSS and other JavaScript libraries such as jQuery. thanks !