I am working on a Raspberry PI and am trying to find a way so that when the end user presses a button a command is executed for the module and and it starts to scan.
It is a Waveshare barcode scanner module.
Sorry I thougth that UART command can only be sent by the TXD-RXD pins. If it's not the case I suppose I can manage it somehow if it's essentially more simple.
I'm not sure what you mean by needing a level converter
On the manufacturer's site (Barcode Scanner Module, 1D/2D Codes Reader) under specifications they wrote "Operating voltage: 5V" and the PI has a 5V (and a 3.3V) pin.
As fkristofb writes and it says in the manual it is 5V ttl. You cannot connect 5v ttl to the gpio pins, otherwise you will destroy the raspberry pi.
I haven't found out what kind of usb adapter comes with your scanner, but it says in the manual that if you want to connect it to a PC, you must use TTL. A usb to ttl adapter gives you a virtual serial port under the pi, but of course it must be a version that supports 5V.
Check under /dev if the supplied usb adapter creates a serial port, if not get such an adapter.