Understanding Web System Behavior

The web system itself is a beginner.

I am studying a web system using Django.

In a desktop system, when a unique code is entered into an input item, the cursor automatically displays the name associated with the code when it leaves the item, but is it the same for a web system?

Example) When you enter a product code item, the product name is displayed next to the item.

If it's the same, how can I make it happen with Django?

Also, if not, could you tell me the basic flow of the web system?

I looked into various things, but I couldn't find a better solution.

Thank you for your cooperation.