So if you are using Modem of a TP-link then it will be very easy to understand because i am going to show the method with tp link but if you are using any other modem also then also the settings will be same with a little difference that the interface will be changed.
Steps to Follow-
1- Open 192.168.1.1 for TP link and who are using other Modems can see the link address from the backside of their Modems,it will be surely written over there.Default username and password is admin and admin respectively.
2-Go to Interface Setup option and then navigate to Wireless option.
3-Now you have to lookup for the Broadcast SSID.
4- Set it to 'No'
5- Save your settings and you are done.
Congratulations, now your Wi-Fi network is hidden from everyone.