CAN'T USE AT COMMANDS

Hey there I'm new on Arduino and esp8266 just keep learning what's going on, I have a problem

I read that I have to update my ESP8266 using some programs(nodemcu) then I upgrade the modul using the sources then I realized that I didn't check if it is consistent or not but I already flashed it.(For knowledge I groundend the GPI O 0)

So now when I wired the breadboard arduino uno and the esp8266 (according to guides of course) I can not send AT commands from serial monitor.When I write AT to serial monitor it responds nothing.
Anybody help?

Which guides ? (links)

How is it wired (schematic)

Which ESP ? (there are lots of different ones)

OK maybe go HERE first and come back and fill in the many missing blank bits.

If you installed the nodemcu firmware then it's to be expected that you can't use AT commands. You need to install the AT firmware if you want to use AT commands.