How do I input the data to screen 1 to scren

Screen 1
How do I make (name) to screen 2 where it says (USER) after clicking next registration?
Screen 2

Use tinydb. Save the details with any tag and retrieve the same in any screen with same tag and same name space

Once the registration over, save the user name in tinydb

Do you have to use TinyDB in these situation or can you use the next screen with start value?

Hello user.

If you would simply want to pass a value to another screen without storing it for future use, you only need to use the next screen with start value block. However, if you would like to store it so that the user can access it even after the app has exited or the device has rebooted, store it in TinyDB. It is not mandatory, just depending on your needs.

How do you pass a value with next screen?

Use the "open screen with start value" block. This can be found in the Control drawer under "Built-in blocks" in the Blocks editor.

See also tip 1 here