I flashed a fresh image onto SD. I do not have HDMI cable. RPi 3 is connected to router. Can I connect to it with out having a monitor? Does OS auto-install and how to get when it installed and started?
If you don't have an Unix-like OS (e.g. MS Windows), you need to install needed commands or additional tools. I determine Raspberry IP addresses in subnet via
nmap -sn 10.42.43.1/24
Either install nmap under cygwin or natively and you should be done: https://nmap.org/book/inst-windows.html