Problem with NodeMCU


I've got a NodeMCU board like this one: NodeMCU

I installed the CH340 driver and esp8266 library, but I still can't upload sketches into it. I tried pushing the Flash button while uploading the code with no success.
I don't know how to communicate with the board. It says:

A fatal error occurred: Failed to connect to ESP8266: Timed out waiting for packet header
*** [upload] Error 2

Could anybody help?