How to use @1x @2x @3x values?

Question

iOS

When developing applications, the @1x @2x @3x values ​​are used.
As far as I understand, it is better to design in @1x, but what resolution does this value correspond to?
If the layouts were created at a resolution of 750 x 1334, then this is @2x? Will this cause problems for the developer?
In general, I do not understand something in these values, I will be very grateful if someone explains. Thank you.

Answer 1

We do it in 1242x2208 - this is iPhone 7+ @3x
Then we scale it up to 640x1136, this is @2x
If there are some fullscreen images, we forget about @2/3x, and write the dimensions directly in the name, the developer will then choose the correct one depending on the device.
It's time to forget about @1x