When you boot up your system for the first time, the GPU will be displayed as Microsoft Basic Display Adapter.
This will indicate that the system has recognized the GPU plugged in the system and after you install the dedicated driver for that GPU, It'll display as RX 580 in Device Manager.
Thank you. One related question:
Should I plug in both GPUs (currently I have two) and install the driver
or install one-by-one i.e. plugging in first install driver and then plugging in second and install driver?
Secondly, do I have to install the driver from executing the .exe file or from the Device Manager individually by right clicking on the device entry?
For two cards, there is no difference (except for time) that you put in the card system together or separately. Nuances can be used when installing 4+ cards.
On the drivers: if it is exclusively mining then it's easier to install the driver from the *.inf file. In this case, no additional software will be installed (Control Center, HDMI audio). If for a full-fledged work, it's better to install from the *.exe file.